execx ==> execxLocalCommand for git libraries in diffusion

Summary:
this was fairly mechanical at the end of the day

note that future/exec got removed by the code generation robots
post this change

Test Plan:
clicked around diffusion a bunch looking for errors.

For a given repo (say http://phabricator.dev/diffusion/BOBALIE/)

• http://phabricator.dev/diffusion/BOBALIE/history/
• http://phabricator.dev/diffusion/BOBALIE/history/origin:master/.arcconfig
• http://phabricator.dev/diffusion/BOBALIE/browse/origin:master/
• http://phabricator.dev/diffusion/BOBALIE/browse/origin:master/.arcconfig
• http://phabricator.dev/rBOBALIEbfede2e8ea9435644968e2e76c0bac8949fb7d06

For a given file (say
http://phabricator.dev/diffusion/BOBALIE/change/origin:master/.arcconfig;bfede2e8ea9435644968e2e76c0bac8949fb7d06)

• history view*
• browse view
• change view

• found a bug where the history view doesn't have the change view in the left

hand UI
will fix laters

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 1095