Add version macros and check function.
* configure.ac (VERSION_NUMBER): New ac_subst. (BUILD_FILEVERSION): Build on all platforms (BUILD_TIMESTAMP): Try to use an ISO string. * src/Makefile.am (extra-h.in): Add new version numbers. * src/versioninfo.rc.in: Update copyright year. * src/version.c: New. (gpg_error_check_version): New API. * src/gpg-error.h.in: Add gpg_error_check_version prototype. * src/gpg-error.def.in: Add gpg_error_check_version * tests/t-version.c: New. * tests/Makefile.am (TESTS): Add t-version.c * src/gpg-error-config.in: s/VERSION/PACKAGE_VERSION/.
All other GnuPG libraries do this, thus we do it here as well.