Speed up nix-shell
Make chroot builds easier to set up

By default, we now include /bin/sh as a bind-mount of bash.
Get rid of "killing <pid>" message for unused build hooks
Add option ‘build-extra-chroot-dirs’

This is useful for extending (rather than overriding) the default set
of chroot paths.
Update manual
Refactor
Move some options out of globals
Doh
Remove unnecessary call to addTempRoot()
install-nix-from-closure.sh: Use https channel if possible
Add support for order-only dependencies
download-from-binary-cache.pl: Respect $SSL_CERT_FILE
nix-install-package: Use extra-binary-caches
Warn about untrusted binary caches in extra-binary-caches
Remove pointless NIX_LOG_TYPE environment variable
Fix warning about non-existant -I directories
Refactor option handling
Handle compound single dash options properly

So now

  nix-instantiate --eval -E '{x}: x' --argstr x -xyzzy

correctly prints "-xyzzy", rather than giving an error.

Issue NixOS/hydra#176.
Use regular file GC roots if possible

This makes hydra-eval-jobs create roots as regular files. See
1c208f2b7ef8ffb5e6d435d703dad83223a67bd6.
nix-log2xml: Handle UTF-8 characters

C++ chars can be negative...