Fix some repository URI handling issues in Git and Mercurial

Summary:
See <https://github.com/facebook/phabricator/issues/467>. @dctrwatson also ran into an issue where we were trying to `setPass()` a GitURI.

  - For Git and Mercurial, properly generate credential URIs where relevant.
  - Don't try to `setPass()` on Git-style URIs.

This isn't perfect but should clean things up a bit.

Test Plan: Added unit tests. Lots of `grep`.

Reviewers: btrahan

Reviewed By: btrahan

CC: dctrwatson, aran

Differential Revision: https://secure.phabricator.com/D7759
Fix two issues with creating Conpherence threads via mail on some configurations

Summary:
Ref T4107. Two issues:

  - With strict MySQL settings, we try to insert `null` into the non-nullable `messageCount` field. Add an `initializeNew...` method.
  - If we don't create a new conpherence (for example, because the message body is empty), we fatal on `getPHID()` right now.

Also, make this stuff a little easier to test.

Test Plan: Used `mail_handler.php` to receive empty conpherence mail, and new-thread conpherence mail.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4107

Differential Revision: https://secure.phabricator.com/D7760
Implement policies in Phragment

Summary: This implements support for enforcing and setting policies in Phragment.

Test Plan: Set policies and ensured they were enforced successfully.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4205

Differential Revision: https://secure.phabricator.com/D7751
Remove patch preview from Phragment version controller

Summary: Patches can exceed the 30 second time out in most PHP installations.  This removes the patch preview from the version controller so that users can still see the information (although they may not be able to download the actual patch).

Test Plan: Viewed a version and saw that the patch didn't appear.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7767