This cleans up some of the mess this code was in. Functions we need to
wrap can now have a standard implementation using WRAP_FUNCTION - that
macro declares the __real and __wrap functions and a wrapped_$func
global variable.
Tests can set that variable to their desired functions and it will be
then be called on demand.
The tests have inadvertent dependencies on each other so let's avoid
those by changing to a system that returns a null-terminated list of
test functions and our test runner iterates over those and forks off one
process per function.
Peter Hutterer
Mihail Konev