Fix xephyr target.

TODO: still need to make the target auto-detect version.
Auto-detect the xephyr version.
Add target check, and prevent unity+xephyr+!precise, which doesn't work.

Closes #78, although this is obviously not ideal.
This can be reinvestigated once xephyr gets egl support.
Merge branch 'master' of git://github.com/michaelorr/crouton

Add e17 as a target.
Install xinput and xterm in the e17 target.
Fix printing target help when run via bash.
Be even more explicit about the right way to open a shell.
Run rc.local upon first entering the chroot.
Implement cursor relaying for xephyr, and separate out C code.

Xephyr can now use cursor acceleration, which looks way better.
Cursor images are not cached, so there's potential performance improvements to
be had.

Splitting out the C code (and dynamically embedding it in the prepare script)
allows C code to be a first-class citizen and more easily testable.

Fixes #58.
Add xterm dependency to xephyr, and nail down the proper version with GLX.
R25 is stable everywhere; update README.
Add keylaunch to xephyr target, and CHROOTETC directory.

Fixes #91
Avoid unmounting the chroot when finishing preparation.
Reduce redundant dependencies.
Only ignore crouton* in the root directory.
Record the version in the chroot and provide a command to query it.
Disable installing Chrome on ARM, since builds do not yet exist.
Properly handle blank targets in target verification step.
Fix typo that stopped -t help and full validation.
Revert keyboard mode after bootstrap; thanks @smibarber!

Fixes #11.