New behavior for FillUpMeasure

[Richard Shann]

At present numeric keypad 8 defaults to FillUpMeasure which duplicates
the current content of the measure until the measure is full. If the
measure is already full it is currently doing the same as keypad Enter
- the FillMeasure command - that is it duplicates the measure.
These are both mainly used when entering rhythms - often the rhythm of
one measure is the same as the next. However, the redundancy of what to
do if the measure is already full can be put to good use, namely to
duplicate two measures (the previous and current one). This enables a
rhythmic pattern that extends over two bars to be repeated.
So I've changed FillUpMeasure to do this rather than just do the same
as FillMeasure.

Richard