Improve performance of ForgetFunctions().

Mostly matters during shutdown, but also module unload.
Small optimization to __PPGeInit().

Small factor in startup time.
Small optimization to func/var import.

Should compare the nid first, of course, faster and less likely to match
anyway.
Cleanup some old typedefs.
Add an interface to read multiple blocks at once.
Implement optimized multi-block reads for iso/cso.

This of course means less fread() calls, and is faster.  It improves load
time even on my desktop.
Minor tweak to avoid some function call overhead.
Switch to a multimap for the hash->function map.
Use std::unordered_multimaps in a few places.
Warning fixes.
Naturally, modern C++ would not build on Symbian.
Typo.
Merge pull request #7046 from unknownbrackets/perf

Improve load and shutdown performance a bit