Added Timeout for poolboy:transaction
Merge commit 'a50e24e3c30b1b0bddc3511eac5661d110885f6a'

Conflicts:
	src/poolboy.erl
Add latest versions of Erlang to our Travis tests
Add back-off ability.
Log connection problems
Add sync workers spawn in case of disabled backoff
Restart poolboy in case of supervisor's death
User defined MFA handle sleep time
Simplify backoff code.
Add backoff test.
Add backoff option to README