BUILD: report commit ID in git versions as well

Currently, the commit ID appears in the sub-version in snapshots, but
when people use the git repository, we only have the commits count,
and not the last commit ID, which requires to count commits when
troubleshooting. This change ensures that unreleased versions also
report the commit ID before the commit number, such as :

      1.6-dev0-bbfd1a-50

Tagged versions will not have this, since the post-release commit count
is zero.
CLEANUP: session: move the stick counters declarations to stick_table.h

They're really not appropriate in session.h as they always require a
stick table, and I'm having a hard time finding them each time I need
to.
MEDIUM: http: add the track-sc* actions to http-request rules

Add support for http-request track-sc, similar to what is done in
tcp-request for backends. A new act_prm field was added to HTTP
request rules to store the track params (table, counter). Just
like for TCP rules, the table is resolved while checking for
config validity. The code was mostly copied from the TCP code
with the exception that here we also count the HTTP request count
and rate by hand. Probably that something could be factored out in
the future.

It seems like tracking flags should be improved to mark each hook
which tracks a key so that we can have some check points where to
increase counters of the past if not done yet, a bit like is done
for TRACK_BACKEND.