[packagekit] pk_backend_finished race issue

[Tom Parker]

I think I'm hitting a race issue in pk_backend_finished, like Grzegorz 
was seeing in the box backend, but this time with the apt backend.

Running a search that you know only returns one result repeatedly 
eventually (3-4 repeats tops) causes a crash with a crappy stacktrace, 
even with all the debug symbols on and "G_DEBUG=fatal_criticals 
G_SLICE=debug-blocks" set in the environment. Adding in a short delay 
(.5s) before the pk_backend_finished removes the problem (>8 repeats, 
all ok).

Richard? Anything more you can do to help this?

Tom