Add full Unicode capability to ports and the default reader

Add full Unicode capability to ports and the default reader

Ports are given two additional properties: a character encoding and
a conversion failure strategy.  These properties have getters and setters.
The new properties are used to convert any locale text to/from the
internal representation of strings.

If unspecified, ports use a default value. The default value of these
properties is held in a fluid.  The default character encoding can be
modified by calling setlocale.

ISO-8859-1 is treated specially.  Since it is a native encoding of
strings, it can be processed more quickly.  Source code is assumed to be
ISO-8859-1 unless otherwise specified.  The encoding of a source code
file can be given as 'coding: XXXXX' in a magic comment at the top of a
file.

The C functions that deal with encoding often use a null pointer
as shorthand for the native Latin-1 encoding, for efficiency's sake.

* test-suite/tests/encoding-iso88591.test: new tests
* test-suite/tests/encoding-iso88597.test: new tests
* test-suite/tests/encoding-utf8.test: new tests
* test-suite/tests/encoding-escapes.test: new tests
* test-suite/tests/numbers.test: declare 'binary' encoding
* test-suite/tests/ports.test: declare 'binary' encoding
* test-suite/tests/r6rs-ports.test: declare 'binary' encoding

* module/system/base/compile.scm (compile-file): use source-code
  file's self-declared encoding when compiling files

* libguile/strports.c: store string ports in locale encoding
  (scm_strport_to_locale_u8vector, scm_call_with_output_locale_u8vector)
  (scm_open_input_locale_u8vector, scm_get_output_locale_u8vector):
  new functions

* libguile/strings.h: new declaration for scm_i_string_contains_char

* libguile/strings.c (scm_i_string_contains_char): new function
  (scm_from_stringn, scm_to_stringn):  use NULL for Latin-1
  (scm_from_locale_stringn, scm_to_locale_stringn): respect character
  encoding of input and output ports

* libguile/read.h: declaration for scm_scan_for_encoding

* libguile/read.c:
  (read_token): now takes scheme string instead of C string/length
  (read_complete_token): new function
  (scm_read_sexp, scm_read_number, scm_read_mixed_case_symbol)
  (scm_read_number_and_radix, scm_read_quote, scm_read_semicolon_comment)
  (scm_read_srfi4_vector, scm_read_bytevector, scm_read_guile_bit_vector)
  (scm_read_scsh_block_comment, scm_read_commented_expression)
  (scm_read_extended_symbol, scm_read_sharp_extension, scm_read_shart)
  (scm_read_expression): use scm_t_wchar for char type, use read_complete_token
  (scm_scan_for_encoding): new function to find a file's character encoding
  (scm_file_encoding): new function to find a port's character encoding

* libguile/rdelim.c: don't unpack strings

* libguile/print.h: declaration for modified function
  scm_i_charprint

* libguile/print.c: use locale when printing characters and
  strings
  (scm_i_charprint): input parameter is now scm_t_wchar
  (scm_simple_format): don't unpack strings

* libguile/posix.h: new declaration for scm_setbinary.

* libguile/posix.c (scm_setlocale): set default and stdio port
  encodings based on the locale's character encoding
  (scm_setbinary): new function

* libguile/ports.h (scm_t_port): add encoding and failed
  conversion handler to port type.  Declarations for new or modified
  functions scm_getc, scm_unget_byte, scm_ungetc,
  scm_i_get_port_encoding, scm_i_set_port_encoding_x,
  scm_port_encoding, scm_set_port_encoding_x,
  scm_i_get_conversion_strategy, scm_i_set_conversion_strategy_x,
  scm_port_conversion_strategy, scm_set_port_conversion_strategy_x.

* libguile/ports.c: assign the current ports to zero on startup so
  we can see if they've been set.
  (scm_current_input_port, scm_current_output_port,
  scm_current_error_port): return #f if the port is not yet
  initialized
  (scm_new_port_table_entry): set up a new port's encoding and
  illegal sequence handler based on the thread's current defaults
  (scm_i_remove_port): free port encoding name when port is removed
  (scm_i_mode_bits_n): now takes a scheme string instead of a c
  string and length.  All callers changed.
  (SCM_MBCHAR_BUF_SIZE): new const
  (scm_getc): new function, since the scm_getc in inline.h is now
  scm_get_byte_or_eof.  This pulls one codepoint from a port.
  (scm_lfwrite_substr, scm_lfwrite_str): now uses port's encoding
  (scm_unget_byte): new function, incorportaing the low-level functionality
  of scm_ungetc
  (scm_ungetc): uses scm_unget_byte

* libguile/numbers.h (scm_t_wchar): compilation order problem with
  scm_t_wchar being use in functions in multiple headers.  Forward
  declare scm_t_wchar.

* libguile/load.c (scm_primitive_load): scan for file encoding at
  top of file and use it to set the load port's encoding

* libguile/inline.h (scm_get_byte_or_eof): new function
  incorporating most of the functionality of scm_getc.

* libguile/fports.c (fport_fill_input): now returns scm_t_wchar

* libguile/chars.h (scm_t_wchar): avoid compilation order problem
  with declaration of scm_t_wchar