* strings.h, deprecated.h (SCM_STRING_COERCE_0TERMINATION_X):

* strings.h, deprecated.h (SCM_STRING_COERCE_0TERMINATION_X):
Moved from string.h to deprecated.h.

* deprecated.c, deprecated.h (SCM_CHARS, SCM_LENGTH): Removed.

* strings.h, strings.c (SCM_MAKE_STRING_TAG): Rename dto
SCM_I_MAKE_STRING_TAG, changed all uses.
(SCM_STRING_CHARS, SCM_STRING_UCHARS, SCM_STRING_LENGTH): Renamed
to SCM_I_STRING_CHARS, SCM_I_STRING_UCHARS, and SCM_I_LENGTH
respectively.  For a short time, the old names are still there as
aliases.  Not all uses have been changed yet, but the ones in
strings.c have.
(SCM_STRING_MAX_LEN): Do not hardcode to 24 bits, compute from
SCM_T_BITS_MAX.
(scm_is_string, scm_from_locale_string, scm_from_locale_stringn,
scm_take_locale_string, scm_take_locale_stringn,
scm_to_locale_string, scm_to_locale_stringn,
scm_to_locale_stringbuf): New.
(scm_c_string2str, scm_c_substring2str): Deprecated by moving to
deprecated.[hc]. Implemented in terms of the new functions above.
(scm_take_str, scm_take0str, scm_mem2string, scm_str2string,
scm_makfrom0str): Reimplemented in terms of the new functions from
above.  They will be discouraged shortly.
(scm_substring): Do not use scm_mem2string.
(scm_i_allocate_string_pointers, scm_i_free_string_pointers): New,
to replace similar code from posix.c, simpos.c, and dynl.c.
(scm_string_append): Use memcpy instead of explicit loop.  Do not
use register keyword.  Use plain 'char' instead of 'unsigned
char'.