fixed typo, purely cosmetic

"executable" was written as "exectuble" and "exectuable"
Merge pull request #721 from SpiritQuaddicted/patch-1

fixed typo, purely cosmetic
Remove simplejson import

"import json" works in Python >= 2.6. simplejson is only useful for Python <=
2.5, which seafile doesn't seem to be targeting.
Merge pull request #718 from jyelee/master

remove related pid file when kill the controlled process among seafile-controller
Merge pull request #723 from brutasse/fix/simplejson

Remove simplejson import
Fix daemon mode in multiple programs under OSX

  - seaf-controller
  - seaf-daemon
  - fileserver
  - seaf-server
Merge pull request #726 from Chilledheart/daemonize_under_osx

Fix daemon mode in multiple programs under OSX