Merge pull request #608 from drinkcat/jessie-xbindkeys

jessie: Install xbindkeys directly from mirror.
This will fix failure of chrome-* target install when it will be installed before a window manager.
Merged installs on one line.
Merge pull request #637 from divx118/master

This will fix failure of chrome-* target install when it will be installed before a window manager.
Create a symbolic link from /usr/local/chroots to /mnt/stateful_partition/crouton:
Makes sure that dev_install does not wipe the chroots.

Also, migrate existing chroots to new directory (transparent to the user, and very
fast as we stay on the same filesystem).
Fixes after review.
Install chroots in /mnt/stateful_partition/crouton/chroots
so we can put other stuff in /mnt/stateful_partition/crouton (e.g. shared directories).