build: introduce git-version-gen
* .gitignore: Add .version.
* Makefile.am (EXTRA_DIST, BUILT_SOURCES): Add $(srcdir)/.version.
Add rules to check NEWS, generate $(srcdir)/.version and
$(distdir)/.tarball-version files.
Change ChangeLog and CREDITS generation rules to depend on
$(srcdir)/.version instead of $(srcdir)/.git/refs/heads/*.
* NEWS: Add dates to recent releases.
* configure.ac (AC_INIT): Use git-version-gen.
(AM_INIT_AUTOMAKE): Remove check-news.
* git-version-gen: Import from gnulib.
* make-dist: Check NEWS.
diff --git a/.gitignore b/.gitignore
index 9ac93c7..ca5703f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
*.o
.deps
.libs
+.version
.*.swp
/ChangeLog