[Vala] vala IDE on OSX

[Serge Hulne <serge hulne gmail com>]

I haven't managed to make a single graphical IDE for Vala work under Mac OS X.

- Under Linux, I use a deprecated (*) version of vtg and valencia (two
plugins for gedit)
- Under Mac, I use vim + Vala plugin for Vim.

The Vim plugin is fine, but it does not provide auto-completion (for
methods, which translates into a serious waste of time).

(*) Because the latest version will only work under Debian Sid (Debian
unstable), which is I cannot use as a stable production system.