Exit cleanly if AppInit2 returns false

Bitcoin-Qt could core dump if application initialization failed in certain ways.

I double-fixed this:
1) qt/bitcoin.cpp now shuts down core threads cleanly if AppInit2 returns false
2) init.cpp now exits before StartNode() if strErrors is set (no reason to StartNode if we're just going to exit immediately anyway).

Tested by triggering all of the various ways AppInit2 can fail, either by passing bogus command-line arguments or just recompiling tweaked code to simulate failure.

This is a partial fix for #2480
translations update 2013-05-04

- updates bitcoin_en.ts and bitcoinstrings.cpp
- removes bitcoin_se.ts
- adds bitcoin_ar.ts
- integrates current translations from Transifex
Merge pull request #2617 from Diapolo/translations

translations update 2013-05-04
Merge pull request #2606 from gavinandresen/threadfix

Exit cleanly if AppInit2 returns false