Implement command handling via event loop.

git-svn-id: https://svn.filezilla-project.org/svn/FileZilla3/trunk@6118 ce1b9ea0-41a8-11dc-9b12-cb80f3b22977
Move event loop to its own thread.

git-svn-id: https://svn.filezilla-project.org/svn/FileZilla3/trunk@6119 ce1b9ea0-41a8-11dc-9b12-cb80f3b22977
Merge remote-tracking branch 'trunk'