Abort on asserts in worker threads.

Abort on asserts in worker threads.

Throwing an exception from worker threads is useless as it is not caught by
our wxUnitTestProtector which only protects the main thread, so abort
immediately to be sure to provide at least some information about the problem
as otherwise nothing may be output at all and the program can end up
deadlocked.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61996 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775