(scm_i_casei_streq): New, for counted strings.

(scm_i_casei_streq): New, for counted strings.

* strings.h, strings.c: (scm_i_string_chars, scm_i_string_length,
scm_i_string_writable_chars, scm_i_string_stop_writing): New, to
replace SCM_I_STRING_CHARS and SCM_I_STRING_LENGTH.  Updated all
uses.
(scm_i_make_string, scm_c_make_string): New, to replace
scm_allocate_string.  Updated all uses.
(SCM_STRINGP, SCM_STRING_CHARS, SCM_STRING_UCHARS,
SCM_STRING_LENGTH): Deprecated.
(scm_allocate_string, scm_take_str, scm_take0str, scm_mem2string,
scm_str2string, scm_makfrom0str, scm_makfrom0str_opt):
Discouraged.  Replaced all uses with scm_from_locale_string or
similar, as appropriate.
(scm_c_string_length, scm_c_string_ref, scm_c_string_set_x,
scm_c_substring, scm_c_substring_shared, scm_c_substring_copy,
scm_substring_shared, scm_substring_copy): New.

* symbols.c, symbols.h (SCM_SYMBOLP, SCM_SYMBOL_FUNC,
SCM_SET_SYMBOL_FUNC, SCM_SYMBOL_PROPS, SCM_SET_SYMBOL_PROPS,
SCM_SYMBOL_HASH, SCM_SYMBOL_INTERNED_P, scm_mem2symbol,
scm_str2symbol, scm_mem2uninterned_symbol): Discouraged.
(SCM_SYMBOL_LENGTH, SCM_SYMBOL_CHARS, scm_c_symbol2str):
Deprecated.
(SCM_MAKE_SYMBOL_TAG, SCM_SET_SYMBOL_LENGTH, SCM_SET_SYMBOL_CHARS,
SCM_PROP_SLOTS, SCM_SET_PROP_SLOTS): Removed.
(scm_is_symbol, scm_from_locale_symbol, scm_from_locale_symboln):
New, to replace scm_str2symbol and scm_mem2symbol, respectively.
Updated all uses.
(scm_gensym): Generate only the number suffix in the buffer, just
string-append the prefix.