fix cpp_plugintests to be at one place
allow run_all to run on target, fixes #11

testcases now read from sourcedir
	no copy to binary at cmake stage required anymore
	they do not write where they read from

writing is into temporary file instead

when installed TARGET_TEST_DATA_FOLDER will be used
(within C use makro BUILTIN_DATA_FOLDER)

should work with cmake 2.6 again?

testdata within directories of pluginname

added
const char *elektraFilename();
void elektraUnlink(const char* filename);