Ensure connect callback is invoked on premature socket hangup

Closes #534
Add unit test for callback on early postgresql disconnect

Test adapted by that provided by Jess Sheneberger in #534
Enable the test for #534 (needs special naming)

This time, I hope, travis will confirm that the fix works with
node-0.10 but not with node-0.8
Have Connection also emit 'end' on stream 'close' event

Should fix missing connect callback call with node-0.8 (#534)
Do not emit 'end' twice from Connection on close
Have stream emit 'close' rather than 'end' for sake of testing
Merge pull request #546 from CartoDB/2.11-ensure-connect-callback

Ensure connect callback is invoked on premature socket hangup