[PATCH] Bug 3281

This patch seeks to avoids race conditions between the AsyncCalls for
the pconn monitoring handlers and lookups pulling pconn up for use.

It adds checks for the read handler, re-implementing the safety feature
which appears to have been attempted and failed at by the earlier use of
read_pending flag. Which _actually_ means SSL code is writing something
that will cause future reads.

It adds checks for the timeout handler, as discussed in bug 3281,
preventing the related type of race from the timeout handler.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE9 or 3.1.15
   Beta testers wanted for 3.2.0.10