Fix issue #659, and cleanup wallet/command-line argument handling a bit #726

This moves all of the "if running over Tor" logic to one place (in init.cpp).

It also fixes issues where settings made in the GUI (like fUseProxy) and stored in the wallet could not be over-ridden in the bitcoin.conf file or command-line, by moving command-line-flag-setting code to after the wallet has been loaded.

That also meant moving the "bind to listen port" to after the wallet was loaded, but that should be OK 99.99% of the time because the lock file is still checked early to protect against accidentally running bitcoin twice.

Forgot to say how I tested:

Ran bitcoind normally to get caught up on the block chain, verify that I get more than 8 connections, and verify (by looking at debug.log) that I connect to the dns seeds and IRC.

Ran Vidalia on my Mac, got connected to the Tor network. Ran bitcoind -proxy=127.0.0.1:2050 VERIFY: I get only 8 connections, and do not connect to dns seeds or IRC.

Then removed addr.dat, and re-ran with -proxy... VERIFY: built-in IP seeding eventually (after trying several non-listening seeds) bootstraps through Tor.