Handle windows paths nicely for cmake

[stonier]

Make sure paths handed off to cmake (in this case catkin/cmake/em/order_packages.cmake.em) are given proper cmake paths (always forward slashes), otherwise cmake falls over trying to parse invalid escape sequences and you get the error of the kind below.

-- Using CATKIN_TEST_RESULTS_DIR: C:/work/ws/build/test_results
-- catkin 0.5.64
-- BUILD_SHARED_LIBS is on
CMake Error at C:/work/ws/build/catkin_generated/order_packages.cmake:58 (set):
  Syntax error in cmake code at

    C:/work/ws/build/catkin_generated/order_packages.cmake:58

  when parsing string

    C:\Python27\lib\site-packages\catkin_pkg\templates\groovy\metapackage.cmake.in

  Invalid escape sequence \P
Call Stack (most recent call first):
  catkin/cmake/catkin_workspace.cmake:35 (include)
  CMakeLists.txt:51 (catkin_workspace)


-- Configuring incomplete, errors occurred!

[wjwwood]

The slashes are correct for Windows, but CMake is falling over on the back slashes.

This is probably not the correct place to fix this, because this function should just return a path, if we need to convert the backslashes to forward slashes for CMake somewhere then we should do it there, not before returning the path.

@dirk-thomas is going to reproduce and find the appropriate place to fix this.

[stonier]

Works here - great.