CMake: handle version of cmake under 2.8.12

- the function target_include_directories was not defined
vle.discrete-time: remove useless typename

With gcc 4.4, typename statement is allowed only for template classes.
all: fix VleUtilsConfig for CMake version < 2.8.12

linked libraries where concatened with ';' which leads to an error for old versions of CMake.
vle.forrester: add a test WITH_GVLE

the subdirectory forrester is added only if GVLE is detected. This avoids to have
a compile error beacause GVLE is missing.
CMake: handle version of cmake under 2.8.12

- Old CMake version are handled for test building, regarding the function
target_include_directories