Lower-ify url before checking against prefix with startswith()
- fixed func call syntax on lower to lower()
- added test cases for trying to test GETS on mixed-case schemas
added tests for mixed-case scheme URLs, changed adapters passing down URLs into urllib3 by lower-ifying them so that the underlying pool manager can effectively pool by scheme as dictionary key
Merge pull request #1385 from ViktorHaag/master

Cope with mixed-case URL schemes (like 'HTTP') by lower-ifying 'url' string before calling startswith() on it