Accept --report-file=FILE to override the default `.output' filename.

Accept --report-file=FILE to override the default `.output' filename.
* NEWS (2.3a+): Mention.
* doc/bison.texinfo (Bison Options): Add an entry.
* src/files.c (compute_output_file_names): Don't override
spec_verbose_file if already set.
* src/getargs.c (usage): Document --report-file.
(REPORT_FILE_OPTION): New anonymous enum member.
(long_options): Add entry for it.
(getargs): Add case for it setting spec_verbose_file.

* build-aux/cross-options.pl: Don't record a short option just because
there's an arg.
* doc/.cvsignore: Add yacc.1.