A CVS Entries file parser

Since we are going to want to look at CVS Entries files to test
cvs2svn, even if not to write it, I have hacked up an Entries file
parser, as part of svn_entry.py. It appears to currently do the right
thing, with the exception of the dates which I don't currently have
the heart to try to translate into SVN/entries style format. I'll
look at that soon.

I've also made get_entries detect wheter it has been passed a CVS or
SVN entries file, and do the right thing either way. I'd like to move
that logic into the class itself (this would also mean that we would
only need one class, instead of two) but I didn't want to muck with
Ben's code too much. If people think that's a good idea, it's just a
cut-n-paste job.

Now to learn about os.walk()
           
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