Always initialize temp variables to fix fatal warnings of GCC 4.8

GCC 4.8 is being strict on possible uninitialized variables.
This may or not may be a temporary solution. Always initializing
variables shouldn't be a problem, apart missing possible bugs
in the generated code.
Bump version suffix
girwriter: Don't emit scope async and notified at the same time

Fixes bug 702180
Update gtk+ 3.0 vapi to latest upstream
gtk+-3.0: mark nullable arguments in ListBox API
gtk+ 3.0 vapi: mark listbox funcs as owned
libusb-1.0: make Device a compact class, other minor changes
glib-2.0: Add version fields and check_version