Catch errors thrown by connect

[xvello]

We had a user submit a PG connstring with ?ssl=off, while this is invalid, it's not failing the parsing, and connect() throws on:

Cannot use 'in' operator to search for 'key' in off TypeError: Cannot use 'in' operator to search for 'key' in off at Socket. (/Users/xavier/git/node-postgres/packages/pg/lib/connection.js:90:19)

Because Connection extends EventEmitter, that exception is not catch-able with a try / catch around the call to client.connect(). I am following on the footsteps of #2569, and making sure that exception is properly caught internally.

Ideally, this ?ssl=off value should trigger a validation error, but:

• I'm not certain not to break compat by adding a stricter input validation
• With this PR, we're possibly covering other edge cases

Added a unit test, that fails if connection.js is not patched: an unhandled exception bubbles up.

[xvello]

Heya @charmander would you have a moment to review this one? It's a pretty small change.

[charmander]

Ideally, this ?ssl=off value should trigger a validation error, but:

• I'm not certain not to break compat by adding a stricter input validation
• With this PR, we're possibly covering other edge cases

This strikes me as the bad kind of defensive programming. An early, strict validation of the value of ssl would be better. We can note the compatibility and the edge cases properly then.