This fixes issue 6563:
https://code.google.com/p/dolphin-emu/issues/detail?id=6563

This PR adds a 2nd map to texture cache, which uses the hash as key. Cache entries from this new map are used only if the address matches or if the texture was fully hashed. This restriction avoids false positive cache hits. This results in a possible situation where safe texture cache accuracy could be faster than the fast one.

Small textures means up to 1KB for fast texture cache accuracy, 4KB for medium, and all textures for safe accuracy.

Since this adds a small overhead to all texture cache handling, some regression testing would be nice. Games, which use a lot of textures the same time, should be affected the most.

CustomTexture: prefetch all available textures

quieted warnings include shadowed variable names and integer extensions.

This drops the "feature" to load level 0 from the custom texture
and all other levels from the native one if the size matches.
But in my opinion, when a custom texture only provide one level,
no more should be used at all.

Various fixes to formatting and whitespace