will work.

Still todo:
* make filterModuleContent use lineNumEnd
* write tests around error conditions
* wire all of this into Run.hs

But now I get a weird linking error.

vagrant at localhost in ~/src/personal/haskell/doctest
$ cabal build
Building doctest-0.9.10...
Preprocessing library doctest-0.9.10...
[14 of 15] Compiling Run              ( src/Run.hs, dist/build/Run.o )
In-place registering doctest-0.9.10...
Preprocessing executable 'doctest' for doctest-0.9.10...
Linking dist/build/doctest/doctest ...
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `s8rZ_info':
(.text+0x12f2): undefined reference to `doctestzm0zi9zi10_TestSelector_extractTestSelectorszuzz0_closure'
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `s8qO_info':
(.text+0xc86): undefined reference to `doctestzm0zi9zi10_TestSelector_zdfShowArgParserErrorzuzdcshow_info'
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `s8Ca_info':
(.text+0xe3c): undefined reference to `doctestzm0zi9zi10_TestSelector_filterModules_info'
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `s8rZ_info':
(.text+0x1303): undefined reference to `doctestzm0zi9zi10_TestSelector_extractTestSelectorszulgo_info'
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `doctestzm0zi9zi10_Run_doctest1_srt':
(.data+0x238): undefined reference to `doctestzm0zi9zi10_TestSelector_extractTestSelectorszulgo_closure'
/home/vagrant/src/personal/haskell/doctest-haskell/dist/build/libHSdoctest-0.9.10.a(Run.o): In function `doctestzm0zi9zi10_Run_doctest1_srt':
(.data+0x240): undefined reference to `doctestzm0zi9zi10_TestSelector_zdfShowArgParserErrorzuzdcshow_closure'
collect2: error: ld returned 1 exit stat

Could do with some tests for arg parsing failures, still.

Also much better error handling.