LANGUAGE should be ignored when LC_ALL=C.
It seems this isn't the case with hg so set both.

The cygwin hg client is a text file with a '#!/bin/python" line.
This cannot run on Windows.

Add a macro to extract information from a Hg work tree much like the
Subversion_WC_INFO macro does for Subversion work tree.

Use the TortoiseHg registry entry as a search path.

Run the convert-help.bash script to convert documentation:

 ./convert-help.bash "/path/to/CMake-build/bin"

Then remove it.

Also teach the CMakeOnly.AllFindModules to verify Hg version detection.