* gen-changelog.py (process_commit): Everything that comes between
the subject line of the commit and the first \t* sequence is
considered to be introductory text. Ignore it when generating the
ChangeLog entry.
* COMMIT-LOG-GUIDELINES: Update the commit log guidelines to
reflect the fact that we can now have introductory text in the
commit log.
Signed-off-by: Dodji Seketeli <dodji@redhat.com>