spice-session: Add field and parsing for URI fragments

As they are not currently checked for, they get tacked onto the end of the last string in the URI, which is obviously wrong.

This change probably only makes sense if the fragment will actually get used for something. I have a subsequent change for virt-viewer that uses a fragment such as #1 or #3 to only show the first or third display, ignoring the others. I want to have one client connect to the first display and another client on another system connect to the second display. I found having both displays popping up in both clients annoying. When only working with one of the displays, I also found it annoying when my daughter would turn on my A/V receiver to play on her games console and the HDMI resync would trigger virt-viewer to reopen the second display when I'd already closed it earlier. Does this sound like a good use of the fragment? Do you think it should have the same meaning across clients? Are we in a position to decide that?

Signed-off-by: James Le Cuirot chewi@gentoo.org