This change depends on the previous one (epilogue unwinder for i386,
http://sourceware.org/ml/gdb-patches/2009-07/msg00099.html).

With the frame unwinder working properly, we can remove the
special case code in the test for "check for subroutine call"
in handle_inferior_event.

Of course that reveals some hidden problems with shared library
calls, so this patch also addresses those.

Michael