Removed lots of unused variables

[mrmonday]

This significantly cuts down on the number of warnings produced when compiling dmd with -Wall.

[WalterBright]

Some of these are necessary for commented out debugging printf's. Unfortunately, that means it's not a straightforward merge.

[mrmonday]

I'll scan through the commit and re-add in the ones needed for debug printfs either commented out or in #if 0 blocks. I thought I managed to get all of them as I went through, seems not though!

[mrmonday]

That took forever D; Been through every diff and re-added variables that were used elsewhere. Also reverted my unintended change to posix.mak.

[WalterBright]

Thanks for doing all that work!

[WalterBright]

Had to revert much of this becase:

1. The C++ compiler would no longer build
2. The D compiler crashes building the library