Improves blueman's inter-process communication.

Improves blueman's inter-process communication.

- Improves stale lock file detection.

  o Blueman will only attempt to send a signal to a possibly running
    instance if the instance is a blueman applet *and* if the current
    user owns the applet.

  o Tested some of the failure scenarios observed by the users thus
    far; blueman didn't crash.

- Some python code rewriting.

  o Minor improvements to the original code.

- Hopefully improved code quality.

  o unit-tested new functions
  o added source code documentation