* verify.c, verify.h: New files.

* Makefile.am (cvs_SOURCES): Add new files.
* main.c: Include "verify.h".
(opt_usage): Add --verify* args.
(main): Process same.
* root.c (new_cvsroot_t): Default verify method options.
(parse_cvsroot): Process same.
* root.h (cvsroot_t): Add verify method options.
* sign.c (get_sign_textmode), sign.h (get_sign_textmode): Export.