BUG/MEDIUM: session: risk of crash on out of memory conditions

In session_accept(), if we face a memory allocation error, we try to
emit an HTTP 500 error message in HTTP mode. The problem is that we
must not use http_error_message() for this since it dereferences the
session which can be NULL in this case.

We don't need the session to build the error message anyway since
this function only uses it to retrieve the backend and frontend to
get the most suited error message. Let's pick it ourselves, we're
at the beginning of the session, only the frontend is relevant.

This bug is 1.5-specific.
BUG/MINOR: peers: set the accept date in outgoing connections

Without this, "show sess" on the CLI reports a wrong age.
BUG/MEDIUM: tcp: do not skip tracking rules on second pass

The track-sc* tcp rules are bogus. The test to verify if the
tracked counter was already assigned is performed in the same
condition as the test for the action. The effect is that a
rule which tracks a counter that is already being tracked
is implicitly converted to an accept because the default
rule is an accept.

This bug only affects 1.5-dev releases.
Merge branch 'master' of http://git.1wt.eu/git/haproxy