Ignore extra arguments passed to Context2D functions.

This is in line with what Chrome, Firefox and IE do.

This is also how most JavaScript functions in Qt behave by default
(for example, TableView::resizeColumnsToContents()).

Task-number: QTBUG-40703
Change-Id: I087221e305dcb5fd6709ad4a99a5163d641faac6
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
V4 JIT: fix stack use below stack pointer

When storing a double value returned from a function call on platforms
where the value wouldn't fit in a register, we used to store it on the
stack and then load it into a FP register. This stack use was done
without first lowering the stack pointer.

For x86 and ARM, the value is loaded directly into the FP register, and
for other non-64-bit platforms it correctly allocates the stack slot.

Change-Id: Idbc260038958a036ac2a7383d845199626decc8e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Silence unused parameter warning in release builds.

Change-Id: I02e5dd0bf511056c876c4e418334cad96657703e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>