strverscmp: migrate from "strverscmp.h" to <string.h> * modules/string (Makefile.am): Add new hooks. * modules/strverscmp (Files): Remove strverscmp.h. (Depends-on): Add string. (configure.ac): Add indicator. (Include): Mention new header. * m4/string_h.m4 (gl_HEADER_STRING_H_DEFAULTS): Provide new defaults. * m4/strverscmp.m4 (gl_FUNC_STRVERSCMP): Inform string module of results. * lib/strverscmp.h: Delete. * lib/string.in.h (strverscmp): Provide declaration, when needed. * tests/test-strverscmp.c (includes): Adjust client. * lib/check-version.c (includes): Likewise. * NEWS: Document the change. Signed-off-by: Eric Blake <ebb9@byu.net>