pluginmanager: change c-level define for hardcoded typelib plugin path

this is now called "TYPELIB_HARDCODED_PLUGIN_PATH"

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>
pluginmanager: override plugin loading locations with env-var "TYPELIB_PLUGIN_PATH"

now the hard-coded plug-lookup-path can be overridden by a environment
variable

the plugins inside the build-folder live in different folders. so we
have to be able to split the env-var at colons to look up a list of
subfolders...

doing like this allows testing the plugins in the build-folder, without
installed them:

    TYPELIB_PLUGIN_PATH=`find build -name 'libtypeLang_*.so' -printf "%h:"` ./build/test/typelib_testsuite

this also works (reproducing the "old" behaviour)

    TYPELIB_PLUGIN_PATH=$ROCK_INSTALL_DIR/lib/typelib ./build/test/typelib_testsuite

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>
CMakeLists: add "TYPELIB_PLUGIN_PATH" env-properties to test-suites

three hardcoded path inside the build-folder where the plugins are located

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>
pluginmanager: add warning on unset env-var

Signed-off-by: Martin Zenzes <martin.zenzes@dfki.de>