Fix invalid session ID bug

This fix should work seamlessly with #2952.
Merge remote-tracking branch 'upstream/master' into beug/session

Conflicts:
	lib/msf/base/simple/post.rb
Use a more correct error message

-1 is a valid session ID, even though it's a fake one.
s/auxiliarly/auxiliary/
Land #2980, @wvu-r7 fix to handle invalid session id on post module runs