Replace CvFILE with GvFILE

[rurban]

Replace CvFILE by GvFILE, where possible.
http://www.nntp.perl.org/group/perl.perl5.porters/2001/05/msg36781.html

Benefit: memory savings. lots of unneeded static strings, some of them even dynamic.

Cost: We need the files in B::C to decide where to split modules. GvFILE should be enough though.
The only problems are: lexical subs, imported functions and anon subs.

For imports: they will have the wrong filename then, the one from the original definition, not the one where the import was done. This is not concern I think
bulk88 came up with a really good patch, I will adopt, I think.

[rurban]

Let p5p handle that first. It's a big API change