INSTALL-xubuntu-12.10: Reverted back to using https protocol for git clone.

I was attracted to using the git protocol for its speed.
I was discouraged from using it for fear that firewalls would
block the git protocol. Reliability is more important than speed,
especially for novices, so I reverted to using the https protocol.
INSTALL-xubuntu-12.10: Use xubuntu-12.10-v1.1 tag instead of v1.1.
INSTALL-xubuntu-12.10 -> INSTALL-xubuntu-12.10-this-is-not-a-shell-script.txt
INSTALL-xubuntu-12.10-this-is-not-a-shell-script.txt: Added code and comments about this not being a shell script.
INSTALL-xubuntu-12.10-this-is-not-a-shell-script.txt: Reworded comments about coping with balky package servers.
INSTALL-xubuntu-12.10-this-is-not-a-shell-script.txt: Improved comment about starting ipython notebook without --pylab option.
INSTALL-xubuntu-12.10-this-is-not-a-shell-script.txt: Fixed quoting bug in echo command.