New way of checking for various LIBUSB names; for legacy version, make sure the symbol 'usb_debug' exists (so-as to not use the 'compat' version).

Update config.guess and config.sub in gr-howoto-write-a-block too

Update script to pull config.* from git repo

formatting change: move break statements

Modify all block factories to use gnuradio::get_initial_sptr.