Proxy support

[bachsio]

Support to run SimpleJPA behind proxy network, (refer to http://code.google.com/p/simplejpa/issues/detail?id=35 )
This would be useful feature because development work in corporate is usually behind a proxy.

Thank so much in advance!

[treeder]

If you can get this into me as a pull request on github, i'll merge it in.

[acemrek]

any improvements on this? will username/password auth be suported? Thanks