PCBC-33: Add support for igbinary

Unfortunately you have to edit Makefile and manually add the
path to the igbinary extension like:

run-tests.php -d extension=/usr/lib/php5/20100525/igbinary.so

If you don't do this running make test will fail due to the
missing symbol.

Change-Id: I4684420b5e2c0a7df8cc7527dbd2ef300486636d
Reviewed-on: http://review.couchbase.org/25701
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>