PGP for Windows

I'd love to use PGP on Windows.

dup of #1890 (closed) and #996 (closed). There is no python interface to use GPG under windows.

http://www.voidspace.org.uk/python/modules.shtml#pycrypto

svn works with e2e encryption (actions button)

(In 6cd8e07f) switch from GnuPGInterface to python-gnupg, so gpg is available under windows. Fixes #5096 (closed), #3615 (closed), #1890 (closed), #996 (closed)