croutonclip: Fix signal handling for bash 4.3

Behaviour of read was changed in bash 4.3, and read does not get
interrupted by signals anymore (affects mostly arch, as trusty
uses dash by default).

Switch to using wait, since that gets interrupted, and we have
children in any case. Incidentally, this simplifies the code
quite a bit.
croutonclip: Refactor triggering code

For some reason bash 4.3.11 (trusty) segfaults often with the
previous version of the code, presumably because traps/sigaction
are not reset properly in children.

We refactor the code to receive signals in a subshell, and print
a line everytime a signal is received. We then read these lines
from the other end of a pipe, and transfer the clipboard.

Tested:
 - arch bash 4.3.24
 - trusty bash 4.3.11 / dash
 - precise bash 4.2.25 / dash (Xephyr)
ubuntu/bootstrap: Patch debootstrap so that it retries downloads

It retries 10 times, which is arguably too many times, but that
should be better than the current behaviour.

Applies cleanly on git HEAD and debootstrap 1.0.61. I will try to
upstream that modification.

Test:
 - Start installer, regularly run `sudo pkill wget` and check
   that the installation still proceeds.
Merge pull request #1025 from drinkcat/croutonclip-fix-signal

Croutonclip: fix signal handling
Update CONTRIBUTORS and simplify generation
Add automated release uploading.
release.sh: improve version checking and support branches
Fix >80-character-wide USAGE
Fix -x and -v passing on systems that output tabs.
Add indirect installer.
Use new download location for croutonversion.
ubuntu/bootstrap: mv -f
Support proxies with indirect installer.
installer/ubuntu/bootstrap: Check if patch applies cleanly

Fallback on original version if it fails.
Merge pull request #1026 from drinkcat/deboostrap-retry

ubuntu/bootstrap: Patch debootstrap so that it retries downloads
Set UID_MIN to 1001 to make sure that useradd does not automatically add users with UID 1000.

This guarantees that UID 1000 is available when post-common adds the main user at the end of the first run of crouton.

Protect GID 1000 in the same way.

Fixes a bug when xbmc is selected during the Arch install (the xmbc user created by the package steals UID 1000).
arch: installer
arch: enter-chroot: source /etc/profile.

Workaround for bug in su/bash, where /etc/profile is not sourced,
even though su is called with '-' (login shell).
See: https://bugs.archlinux.org/task/31831
This is necessary to get /usr/local/bin in the PATH, and setup the
correct locale, among other things. This is not necessary in Ubuntu,
as these are set by /etc/pam.d/su
arch: core/post-common.
arch: x11/xephyr/x11-common