Try to fix testsuite

When configuring tools/typelib a c-level define "TYPELIB_PLUGIN_PATH" is added to the compile-flags of "pluginmanager.cc" which hardcodes the _install_ folder of typelib by default [1].

So typelib (and its testsuite) will _only_ run against the installed plugins? And the testsuite happily ignores local compiled plugins inside the build-folder? So testing without contaminating the install-folder is by design impossible?

i have a local commit to use some env-var to override with a single path (for in-build testing) but it does not help, since all the plugins are in seperate folders... uaaargh... WHY U NO SIMPLE?

[1] https://github.com/orocos-toolchain/typelib/blob/master/typelib/CMakeLists.txt#L9