For the same reasons as set_config is being moved to the global scope,
we're moving set_define to the global scope here. An additional change
is that set_define is now part of the sandbox itself instead of being
defined within the sandbox, which makes it share the implementation
details with set_config.
The way set_config is set currently makes it difficult to introspect
moz.configure files to know what configuration items are being set,
because they're hidden in the control flow of functions.
This makes some of the moz.configure more convoluted, but this is why
there are templates, and we can improve the recurring cases afterwards.
Mike Hommey
Carsten "Tomcat" Book