[Tracker] Small bug

[Gergan Penkov <gergan gmail com>]

Hi all,
I'm sorry for posting so much problems around, it does not mean that
the tracker does not work, simply I'm testing it more extremely
probably, doing things with it which were not intended to be done :)
So today playing with it, I was able to crash it reproducibly with the
following:
tracker-meta-folder --help
I have always a second terminal, where the trackerd is running:

trying to reacquire it
trying to reacquire it - success
Warning - parameter 0 is null
*** glibc detected *** trackerd: munmap_chunk(): invalid pointer:
0x0841ef6f *** Received fatal signal Aborted so now aborting.
total allocations = 8127 , total deallocations = 8127

the two messages in the beginning have been added from me, just simple
tracker_log statements to look how the user_request mutexes are acquired
and released. I don't know where the glibc detected and the signal
Aborted come from, but this leads to very bad state as the mutex is
still locked and the trackerd could not die graciously, it should
be killed.

Cheers
Gergan