[GH #910] make clean on linux|darwin even without lib/Parrot/Config/Generated.pm
[install] Remove duplicate wrong install_config.o [main]lib

We need only src/install_config.o [main]lib for mod_parrot
[GH #910] install: Add all dynext libs with load_ext, all exes

More sanity checks.
Fixes select missing on windows, gziphandle without has_gzip,
mixed windows path slashes.