added recursive mutex to protect class initialization, default interface

added recursive mutex to protect class initialization, default interface

2008-02-05 18:52:07  Tim Janik  <timj@imendio.com>

        * gtype.c: added recursive mutex to protect class initialization,
        default interface initialization and per-class interface construction.
        a lock to this recursive mutex is held during user callback invocations
        such as initializers or finalizers, effectively allowing only one thread
        to run class/interface initializers/finalizers at a time.
        also made misc fixups. this fixes:
        Bug 64764 - Class initialization isn't thread safe.

svn path=/trunk/; revision=6454