Preload OpenSSL DLLs on Windows.

Add code to _setupQtDirectories that will preload the OpenSSL DLLs if
they are included in the PySide package.  It uses a trick of temporarily
modifying the PATH so Qt's QSystemLibrary will be able to find them.

Change-Id: I67b56642ef74444f19806b52c6a1080dc6d92996
Reviewed-by: John Ehresman <jpe@wingware.com>