If keywords are matched on the start/end of words then
keywords are also matched if they are surrounded by dashes
or underscores. For example the keyword with is highlighted
in geany-with-vte. When matching on the start/end of symbols
the keyword is only highlighted if it is not part of an other
identifier.

Emacs 24.1 introduced the notion of "basic major modes" and among these
is prog-mode, see section "23.2.5 Basic Major Modes" in the Emacs
manual. The prog-mode basic major mode is recommended as a base for
derived major modes that are intended for editing source code.

- Use define-derived-mode to declare nix-mode
- Use autoloads to ensure nix-mode is usable (and enabled) without needing `require`
- Use set + make-local-variable instead of longer 2-step equivalent

Signed-off-by: Ricky Elrod <ricky@elrod.me>

http://hydra.nixos.org/build/10170940

In Nixpkgs, the attribute in all-packages.nix corresponding to a
package is usually equal to the package name.  However, this doesn't
work if the package contains a dash, which is fairly common.  The
convention is to replace the dash with an underscore (e.g. "dbus-lib"
becomes "dbus_glib"), but that's annoying.  So now dashes are valid in
variable / attribute names, allowing you to write:

  dbus-glib = callPackage ../development/libraries/dbus-glib { };

and

  buildInputs = [ dbus-glib ];

Since we don't have a negation or subtraction operation in Nix, this
is unambiguous.

fixes to nix-worker systemd service descriptor: - remove commented-out lines - register the file for distribution in Makefile.am

    x.y.z or default

  (as originally proposed in
  https://mail.cs.uu.nl/pipermail/nix-dev/2009-September/002989.html).

  For instance, an expression like

    stdenv.lib.attrByPath ["features" "ckSched"] false args

  can now be written as

    args.features.ckSched or false

this enables (require 'nix-mode)

  much as possible.  (This is similar to GNU Make's `-k' flag.)

* Refactoring to implement this: previously we just bombed out when
  a build failed, but now we have to clean up.  In particular this
  means that goals must be freed quickly --- they shouldn't hang
  around until the worker exits.  So the worker now maintains weak
  pointers in order not to prevent garbage collection.

* Documented the `-k' and `-j' flags.