[Vala] Vala posix profile

[pancake <pancake youterm com>]

I just did a little test using cairo with the posix profile of Vala. You can read the code at code.valaide.org

The first issue I get is that stdio.h is not included until you use a function like print() which is a bit 
annoying because vala already places some defines before the code (cairo_destroy,,..)

I think stdio.h should be included when using the --profile=posix 

The other bug I found is that Vala places a g_return_if_fail if I pass an instance as argument to a 
function... This shouldnt be done on posix. Or at least provide a non glib dependant code like redefining 
this or just use assert()

What do you think about these changes?

Thanks