* strings.h: don't use SCM_P. don't include <string.h>.

	* strings.h: don't use SCM_P.  don't include <string.h>.
	* error.c, gh_data.c, ports.c, script.c, strop.c: include <string.h>.

	* strings.c (scm_string_ref): make the 2nd argument compulsory.
	previously it defaulted to zero for no good reason that I can see.
	use a local variable for SCM_INUM (k).  replace
	SCM_VALIDATE_INUM_DEF with SCM_VALIDATE_INUM_COPY.

	(scm_makfromstr): cosmetic changes.

	(scm_string): Accept only chars in the list, not strings, for
	conformance to R5RS (particularly for list->string, which is
	supposed to be the inverse of string->list.)  remove
	SCM_DEFER_INTS/SCM_ALLOW_INTS, which is unnecessary since
	scm_makstr handles the cell allocation.  when reporting wrong-type
	arg, don't report the position as 1.

	* posix.c (scm_init_posix): intern PIPE_BUF if it's defined.

	* boot-9.scm (find-and-link-dynamic-module): pass strings, not symbols,
	to string-append.