maint: generate full and correct ChangeLog.

maint: generate full and correct ChangeLog.

* gnulib: Updated to pick up gitlog-to-changelog multi-author
support.
* gl/build-aux/gitlog-to-changelog.diff: Use gnulib-rejected
patch for '(tiny change)' support.
* Makefile.am (ChangeLog): Use gitlog-to-changelog --amend=F
option.
* libltdl/config/git-hooks/commit-msg: New commit message hook
for git.
* libltdl/config/git-log-fix: New file, with ChangeLog fixes.
* HACKING (Using git): Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>