Add support for no_proxy to HTTP connections

In addition to the http_proxy environment variable, most url
handlers support a no_proxy environment variable, containing a
comma-delimited list of domains to ignore.

Solves Issue #1600
Fix no_proxy support, add https support, add tests

This adds support for https, fixes a broken reference,
and adds two unit tests.

Solves Issue #1600
Remove extra whitespace
Cleanup no_proxy environment variable during tests
Merge remote-tracking branch 'holzman/issue/1600' into develop