Convert, combine, split

[Valentin Ungureanu]

A new patch on savannah:
http://savannah.nongnu.org/patch/?func=detailitem&item_id=3746

It adds three commands from version 0.6: convert to curves, combine
beziers, split beziers and some tests for them.

Unlike in version 0.6, they can be applied even if the selection
contains other object types than those strictly required, they just act
on the proper objects and ignore the others.

The "Combine Beziers" command now converts objects where required, so
it's possible to select and combine two rectangles. Unlike in version
0.6, this new combined curve stays in the layer/position of the first
object in the selection instead of being inserted in the active layer.

In version 0.6 the "Convert To Curve" command required that a single
object is selected, now it can be applied to multiple objects at once.


Valentin