gui: fix non-sticking proxy setting #3005

Addresses the last (I believe) work-item in #2371.

I'm unsure of the correct fix here, but I hope this can at least get some discussion going. This change at least fixes the problem on the surface. Here's the summary as I see it:

There's a mix of current-proxy-setting and saved-proxy-setting logic. Assuming the proxy is currently enabled: User unchecks the proxy checkbox, hits apply, the dialog checks to see what the new proxy setting should be, GetProxy() returns true because it's currently enabled, check remains in the checkbox, user is confused.

Logically (to me) it makes sense to be checking the setting rather than the current runtime values, as the setting should reflect what user sees on next restart. But there are plenty of other GetProxy()/SetProxy() calls, so I'm inclined not to trust that line of reasoning.

Summary fail. This attempts to fix an issue in bitcoin-qt where checking or unchecking the "Connect through SOCKS proxy" box does not work as expected. It's easily reproduced by enabling/disabling and clicking 'apply'.

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/b07659bf46deb7e81428aea64ac600975a6360ed for binaries and test log. This test script verifies pulls every time they are updated. It, however, dies sometimes and fails to test properly. If you are waiting on a test, please check timestamps to verify that the test.log is moving at http://jenkins.bluematt.me/pull-tester/current/ Contact BlueMatt on freenode if something looks broken.

That whole proxy stuff in current Bitcoin-Qt settings is IMHO a mess, because we try to change it on the fly, which doesn't even work for bitcoind, you may want to take a lookt at #2612.

Fixed by #3347