Fault injection is expected to be *very* cheap, we even enable it on
production builds. That's why I was very surprised when I saw 'perf' report
that FaultInjector_InjectFaultIfSet() was consuming about 10% of CPU time
in a performance test I was running on my laptop. I tracked it to the
FaultInjector_InjectFaultIfSet() call in standard_ExecutorRun(). It gets
called for every tuple between 10000 and 1000000, on every segment.

Why is FaultInjector_InjectFaultIfSet() so expensive? It has a quick exit
in it, when no faults have been activated, but before reaching the quick
exit it calls strlen() on the arguments. That's not cheap. And the function
call isn't completely negligible on hot code paths, either.

To fix, turn FaultInjector_InjectFaultIfSet() into a macro that's only
few instructions long in the fast path. That should be cheap enough.
Reviewed-by: NAshwin Agrawal <aashwin@vmware.com>
Reviewed-by: NJesse Zhang <jzhang@pivotal.io>
Reviewed-by: NAsim R P <pasim@vmware.com>