Handle SIGCHLD properly for multiprocessing

This commit should fix #101 by enabling a special SIGCHLD
handler for when multiprocessing is in use.  The handler
simply calls `multiprocessing.active_children()` (which in
turn calls `_cleanup()`) upon receiving a SIGCHLD.  Now,
the `fallback_SIGCHLD` is only called when `multiprocessing`
is not in use.  See also #95.
Merge pull request #102 from DirectXMan12/master

Handle SIGCHLD properly for multiprocessing (fixes #101)
Fix syntax errors in other/websockify.rb
Merge pull request #103 from dellsystem/master

Fix syntax errors in other/websockify.rb
Fix crash when an import is missing

self.msg is not available when checking the imports.

I had the problem on a host where numpy is missing (python 2.7.3).
Merge pull request #104 from stevschmid/patch-1

Fix crash when module is missing
Merge remote-tracking branch 'upstream/master'