Adding OS X .dmg build scripts.

Simply place this into the root of your nodejs git working copy and
run ./tools/osx-dist.sh. It will create an dist-osx folder which will
comprise of the resulting .dmg file (install path is
/usr/local/nodejs with symlinks added to /usr/local/bin) along with
other files used during its construction.

$ ls -1 dist-osx/
nodejs-v0.1.26-11-gcd6397c
nodejs-v0.1.26-11-gcd6397c.dmg
nodejs-v0.1.26-11-gcd6397c.pkg
nodejs-v0.1.26-11-gcd6397c.plist

The resulting installed package is going to be visible using the
OS X 'pkgutil --packages' command. You can even safely uninstall
sudoing 'pkgutil --unlink org.nodejs.NodeJS-...' and subsequently
let the system forget about the package being ever seen by
'pkgutil --forget org.nodejs.NodeJS-...'.

Here is the current package ID I have installed:

$ pkgutil --pkgs | grep node
org.nodejs.NodeJS-v0.1.26-11-gcd6397c

Use this patch freely without hesitation.

Signed-off-by: Standa Opichal <opichals@gmail.com>