Clear the symbol map between each test.

This way we could, for example, test function replacement properly.

Actually slows down tests because it spends more time correctly
determining the function boundaries.
Spend a bit less time in Read_Instruction on load.
Speed up MIPSGetInstruction() by 35%.

It's not that hot, but gets called a lot when loading modules / running
tests.  Well, and also interpreter.

Some of the previous checks were just not necessary (we never have Rese in
the tables, for example, and let's just not.)
Turns out this difference began in mpeg.prx 0105.
[Xbox] Missings files
[Common] add unsigned long
[xbox] 360 support for Core
[core] 360 fixes
[Xbox] fixes
[core/common] cpu/gpu threading
[Xbox]
[Xbox] Network disabled for xbox
[sceIo] 360 thread fixes
[jit] try to implement fpu round
[Jit] don't recompile with slow memory
[PPC] update/fix
ppcjit: Int_Cache() now does stuff, use DISABLE.
[jit] save fpr, less crashes ?
Add ppcEmitter.cpp/h to the MSVC project.

So that it's searchable/etc.
[jit] round fpu