Replace pcre-light by regexp-tdfa.

[Toxaris]

The pcre-light package is a binding to a C library, so it is non-trivial to compile on Windows. I think this is the main reason for the "Unix systems only, currently." warning in the package description. In this pull request, I replaced pcre-light with regexp-tdfa (which is pure Haskell), and it compiles fine and seems to work.

Open Questions:

• I ignore the ungreedy options. Are they important?
• regexp-tdfa implements Posix regexps, but pcre-light implements Perl-style regexps. Is the difference important for ghc-core?
• Is regexp-tdfa a good choice? It would be easy to use any other library that implements the common regexp API.

[erikd]

ghc-core doesn't compile with current GHC git HEAD because pcre-light doesn't compile.

[Toxaris]

I see. What's the easily portable regular expression library of choice, then?

[erikd]

'regex-tdfa' or any of the others should be fine.

[Toxaris]

Oh, looks like I didn't see. So this patch is good for two reasons: works on Windows, works with ghc head?

[erikd]

Unfortunately regex-tdfa is broken with ghc HEAD. I've emailed the author.

I still think regex-tdfa is a good choice for this project.

[Toxaris]

Roman Cheplyaka forked and repaired regex-tdfa. See discussion and fork.

[erikd]

Gah! That's messy!

Roman has created a new package, same as the old package with a minor fix, but that package is only a temporary solution until he fully takes over the old package at which point the new/temporary package dies.

I can understand why he did it, but ....... gah!

[erikd]

Upstream regex-tdfa has been fixed for the pending ghc-7.8 release so ther eis no reason to use regex-tdfa-rc.