diffutils now uses git

[Jim Meyering]

The GNU diffutils now use Git for version control.

Here's the gitweb link:

    http://git.savannah.gnu.org/cgit/diffutils.git/

Converting this repository from CVS to Git was a challenge,
due to the unusual way in which some change sets (in particular deletions)
were recorded.

Well, first, just to get parsecvs to process all of the ,v
files required a handful of NULL-dereference fixes to that tool.
Then, the resuling git repository had no tags, and a clone
had many files that had been removed from cvs.

I inserted a single commit to remove all of those files, making
it so a clone the git repo was identical to the latest checkout
from cvs.

For now, I have added a single signed tag, for the most recent
release.  I'll add the remaining ones later.

I've made some changes to start making diffutils work with
e.g., "make syntax-check" and some other things like I've done
with coreutils.  Here's a summary of the changes

    build: update build/release infrastructure
    maint: require newer automake, new non-major version string, dist-xz
    maint/sc: remove useless if-before-free tests
    maint: rename ChangeLog to ChangeLog-2008
    maint/sc: remove cast of xmalloc return value
    maint/sc: enable check for duplicate "the"; fix one
    maint: record previous version
    maint/sc: enable check for CVS keyword expansion
    maint/sc: enforce "file system" spelling
    maint/sc: use STREQ, not strcmp(a,b) == 0
    maint/sc: enable the po check
    maint/sc: enable two config.h-checking rules
    maint/sc: enable check for unmarked diagnostics
    build: rely on gnulib's mbrtowc module
    maint/sc: enable the space-TAB check
    build: rely on gnulib's progname module
    maint/sc: enable the m4 quote check
    admin: update all copyright notices to include the year 2009
    build: generate ChangeLog (from git logs) into distribution tarball
    maint: tell git what it can ignore
    maint: use a git submodule for gnulib