Modified error handling for OpenGL backend, now error messages should be visible.
Corrected Doxygen comments notation.
Although CMake keeps time stamps to remember how far it got in an ExternalProject_Add()
build, it throws the time stamps away when there are edits to the CMakeLists.txt portion
pertaining to the external project.  Only a 'make clean' would remove the untarred tree.
This patch removes the need to do a make clean when changing the ExternalProject_Add()
text pertinent to patching.

Fixes bug 1250222 in KiCad-Winbuilder
Commit Launchpad merge request 194664.

* Modify error handling for OpenGL backend.
* Correct Doxygen comments notation.
Completion of DIALOG_FP_PLUGIN_OPTIONS
change