add ssl detection to ParseURL and test accordingly

[hcliff]

This would be a pre-requisite to extending mgo with baked in PEM support etc... but also avoids users having to separately parse their urls to see if connection string uses SSL.

I'd like to keep working on this but:

1. I'm unclear on the scope of mgo - is a TLS dialer, pem reading/parsing something you'd like to include (I've seen other libraries have a pemFilePath url param)?
2. I'm having issues getting the test suite to run and as such my tests here are speculative
   here's my supervisord output http://pastebin.com/GqEGFc60