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.
Handle debootstrap download failures better, and try a backup source.
Use --one-file-system to avoid mishaps in delete-chroot.
Check and enforce username validity before passing it to adduser.
Symlink /dev/.udev to /run/udev for new udev

The version of udev on raring and later uses `/run/udev` instead of
`/dev/.udev`.

Fixes #110
Better linking of /dev/.udev to /run/udev

Use -T to replace /run/udev symlink rather than mistakenly treating it
as a directory, and avoid deferencing symlink with fixabslinks
Merge pull request #113 from smibarber/master

Fix for udev /run/udev in raring
Add support for specifying proxies with -P.
Sanity: don't make a new chroot if -u is specified.
-b: only redirect IOs that are associated with terminals.
Avoid ambiguities for /dev/shm symlink.
Don't remount /tmp dev+exec; instead just create a temporary tmpfs.
Clean up traps: use ' instead of \".
Don't pass stdin to rc.local.
-b: properly pass through stdin if it is not a terminal.
Limit retries in downloading debootstrap, and print wget messages.
Fix command escaping; quotes and whatnot should work fine.
Converted pkgdetails to mawk; speeds up install by at least 5 minutes.

Also fixes a bug in detecting dependencies; output now matches pkgdetails.c.
This fixes Debian installs (at least the bootstrap phase).

Timed the first part of the install via:
sudo true; time sudo sh -e crouton -d -f/dev/null 2>&1 | grep -q adduser

Results:
Pixel: 5m11s -> 16s
ARM: 7m35s -> 6.5s
Cr48: 9m58s -> 7s

Basically, debootstrap is back to being network-limited as it should be.

Interestingly, the mawk version is generally faster than the c version (up to
2x) due to mawk compiling regexes.