contrib/hooks: add sample post-receive hook using agefile

One of the most frequent questions on the mailing list relates to the
idle time in the repository list.  The answer to this is to use the
"agefile" feature to calculate the time of the last change whenever the
repository receives changes.

Add a sample post-receive hook in a new "contrib" directory so that we
can just point people at the repository in the future.

Signed-off-by: John Keeping <john@keeping.me.uk>
Merge branch 'diff-summary' into pu

* branch diff-summary:
  ui-diff: add "stat only" diff type
  Change "ss" diff flag to an enum
  ui-shared: remove toggle_ssdiff arg to cgit_diff_link()
  ui-shared: remove toggle_ssdiff arg to cgit_commit_link()

Suggested-by: Konstantin Ryabitsev <mricon@kernel.org>
Merge branch 'time-tooltip' into pu

* branch time-tooltip:
  ui-shared: show absolute time in tooltip for relative dates

Add the absolute time as the title for spans containing a relative date.
Merge branch 'contrib-hook-agefile' into pu

* branch contrib-hook-agefile:
  contrib/hooks: add sample post-receive hook using agefile

Add an example post-receive hook to configure the agefile.
Merge branch 'jk/compat-timegm' into pu

* branch jk/compat-timegm:
  compat/timegm: new compat function for systems lacking timegm()

Submitted to cgit@hjemli.net but not applied.

Need to see if there is an alternative to introducing a compat function.
Doing the back and forth in the local timezone is mostly good enough,
but doesn't handle DST correctly.
Merge branch 'log-follow-files' into pu

* branch log-follow-files:
  log: allow users to follow a file
  shared: make cgit_diff_tree_cb public

In its own branch upstream.

# Conflicts:
#	ui-log.c
Merge branch 'test-improvements' into pu

* branch test-improvements:
  WIP

WIP improvements to make the test suite more robust.
Merge branch 'scan-exclude' into pu

* branch scan-exclude:
  Add scan-exclude option to filter out repositories

An experiment to handle a certain use case.  Probably not desirable.