git clone on Mac

[Steven Shaw]

Cloning this repository on Mac with a case-insensitive filesystem doesn't work because of the files TMVar.hs and tmvar.hs (one of which is a soft-link to the other).

I propose to put these "miscmodules" into a subdirectory with soft links back to the parent directory. This way the filenames are still the same as in the book but the code can be used on a Mac with the default filesystem.

[Steven Shaw]

I submitted PR #16.

[Franklin Chen]

This appears fixed now, so can be closed.

[Simon Marlow]

Thanks!