Disable color extensions in Mercurial

Summary: Mercurial has a --color flag which disables the use of ANSI colors. Use
it to prevent "hg diff" from giving us colorized diff output.

Test Plan: Ran "hg diff --color never", verified it disabled ANSI color in diff
output.

Reviewers: Makinde, jungejason, nh, tuomaspelkonen, aran

Reviewed By: aran

CC: aran

Differential Revision: 1079

src/repository/api/mercurial/ArcanistMercurialAPI.php

@@ -226,6 +226,7 @@ class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
   private function getDiffOptions() {
     $options = array(
       '--git',
+      '--color never',
       '-U'.$this->getDiffLinesOfContext(),
     );
     return implode(' ', $options);