Merge IR::Module and IR::Function.

Merge IR::Module and IR::Function.

V4 compiles one function at time. There is no reson to keep
IR::Module and IR::Function as separate classes.

Change-Id: Ia6bf971d0d499b14847c3ca725f9cdf5c7e3916c
Reviewed-on: http://codereview.qt.nokia.com/3784
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>