Restore tap-to-click when switching to the chroot with Xephyr.

When typing, Chromium OS disables tap-to-click. This normally gets re-enabled
once the mouse moves, but when launching or switching to a chroot, Aura does not
get any more mouse movement events and so cannot re-enable tap-to-click. We now
do so manually upon window switch, for an arbitrary number of trackpads.

Fixes #38.
Add default locale installation
Make setting locale conditional
Fix formatting and generate only en_US.UTF-8 locale
Fix quotes for non-expanding strings
Merge pull request #133 from x3qt/master

Configure system locale with an arbitrary default to avoid issues.
Fix keyboard mode slightly earlier on upgrade.
Synchronize localtime between Chrome OS and host OS:
 - bindmount /var/lib/timezone
 - During installation, link /etc/localtime to /var/lib/timezone/localtime
Update /etc/timezone in enter-chroot, by guessing its value from
the current /etc/localtime.
Add -T to the creation of /etc/localtime symlink, in the unlikely
case where /etc/localtime is a directory.
Revert "Update /etc/timezone in enter-chroot, by guessing its value from"

After discussion, updating /etc/timezone is not necessary, and even
possibly harmful, as Ubuntu would erase /etc/localtime upon tzdata
upgrade if /etc/timezone exists.

This reverts commit 94566f369f2e34ca2688b8584ff3c6955561b131.
Document why we are removing /etc/zoneinfo from the guest OS.
Check that the link /etc/localtime points to is a valid timezone in the guest OS.
Simplify timezone sanity check.
ChromeOS -> Chromium OS
Properly copy symlinks when installing files.
Add double-e parameter to mount-chroot to change the passphrase.
Support passing two -e's to the installer.
Add edit-chroot command for managing chroots.

delete-chroot is now just a symlink to edit-chroot.
Don't chmod copied symlinks.