Added arcanist linters and cleaned errors and warnings

  Arcanist (arc) will now always run linters before uploading any new
  commit to Phabricator. All errors/warnings (or their absence) will be
  shown in the web interface together with a explanation by the commiter
  (arcanist will ask the commiter if the build was not clean).

  The linters include:
    - clang-format
    - spelling check
    - permissions check (aka. chmod)
    - filename check
    - merge conflict marker check
  Note, that their scope is sometimes limited (see .arclint for
  details).

  This commit also fixes all errors and warnings these linters reported,
  namely:
    - spelling mistakes and typos
    - executable permissions for various text files

Differential Revision: http://reviews.llvm.org/D4916