Allow files with more than 4GB

[J0s3f]

Please include this patch to allow large file patches

[jjwhitney]

J0s3f,

There are some good changes in Bernd's patches, but also some that I can't merge.

• Using 64-bit integers for file positions causes efficiency problems and should be done only for files > 4GB. (Generics might be the solution here?)
• fseeko and ftello do not always use 64-bit integers, so we need to use fseeko64 and ftello64 instead.
• Backward compatibility should be maintained for previous patches (for a while, anyway).
• The ability to set granularity of diffs is important for finding changes in text files, so that cannot be removed (TOKEN_SIZE).
• We shouldn't require the source files to be read into memory all at once.
• The unmatched data in the patch should be kept separate so that compressible data is in contiguous blocks. I'm not sure what the motivation was for changing that?

I'll go through the changes to get fixes or improvements, but the merge as a whole is too aggressive.

Thanks!