Update translations from Transifex:

 - Croatian
 - Hungarian
 - Japanese
Update files for 1.7.4.
Update docs/Release.txt.
Set MPC_NIGHTLY_RELEASE to 1.
Fix race warning

CID 1201438
Resolve static initialization order fiasco
Add simple readers-writer lock implementation
Discard .ini cache when it's not being accessed

Refs #4193
Use the right prefix for bool variable
StatusBar: paint children bypassing the queue

Fixes rare flickering.
MainFrame: call OnGetMinMaxInfo() before resize
Cosmetics