#8733: adds aliaser script

Fixes issue #8733 :

This Applescript creates an OS X alias to the current version of the Julia executable. This will have to be updated every time there's a new version with the filename of the current Julia `.app`.

For legibility, as `scpt` is a binary format Github doesn't like much, here's the source:

```applescript
-- Julia aliaser

set juliaVersion to "0.4.0-dev-d066c3f061"
set aliasingJuliaScript to "ln -s /Applications/Julia-" & juliaVersion & ".app/Contents/Resources/julia/bin/julia /usr/local/bin/julia"

try
	do shell script aliasingJuliaScript with administrator privileges
on error errStr number errorNumber
	if the errorNumber is equal to 1 then
		display dialog "A Julia alias already exists under /usr/local/bin. Would you like to update the alias to the currently installed version?" buttons {"Yes", "No"} default button 1
		if result = {button returned:"Yes"} then
			do shell script "rm /usr/local/bin/julia" with administrator privileges
			do shell script aliasingJuliaScript with administrator privileges
		end if
	end if
end try
```