Subject: [PATCH] fix some performance gaps in Xace

The XaceHook function is used in several hotpaths.
The problem with it (performance wise) is twofold:
 * The XaceHook function has a big switch() statement for the hook number in it
 * The XaceHook function uses varargs to reassemble the final dispatch arguments again

Both are expensive operations... for something that is known at compile time

This patch turns the hotpath XaceHook call into a direct call to avoid
the switch and varargs; this gives me over 10% performance gain
on the x11perf benchmark.