FindHg: Run hg with C locale when querying its version.

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

Modules/FindHg.cmake

@@ -63,11 +63,21 @@ find_program(HG_EXECUTABLE
 mark_as_advanced(HG_EXECUTABLE)
 
 if(HG_EXECUTABLE)
+  set(_saved_lc_all "$ENV{LC_ALL}")
+  set(ENV{LC_ALL} "C")
+
+  set(_saved_language "$ENV{LANGUAGE}")
+  set(ENV{LANGUAGE})
+
   execute_process(COMMAND ${HG_EXECUTABLE} --version
                   OUTPUT_VARIABLE hg_version
                   ERROR_QUIET
                   RESULT_VARIABLE hg_result
                   OUTPUT_STRIP_TRAILING_WHITESPACE)
+
+  set(ENV{LC_ALL} ${_saved_lc_all})
+  set(ENV{LANGUAGE} ${_saved_language})
+
   if(hg_result MATCHES "is not a valid Win32 application")
     set_property(CACHE HG_EXECUTABLE PROPERTY VALUE "HG_EXECUTABLE-NOTFOUND")
   endif()