Bug #430: Use the function "list(APPEND ...)" at more places in build scripts

The command "list(APPEND ...)" can be executed more efficient than the setting
of variables as before. Specific support was added by the tool "CMake 2.4".
http://cmake.org/Wiki/CMake_Performance_Tips#Use_LIST.28APPEND_....29

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Merge branch 'appending_of_elements_to_CMake_lists' of git://github.com/elfring/pcl