proposed patch for embedded runs

Hi,

Currently, editing a chart is not reliable because the graph guru is not
modal and the current code assumes that the chart remains selected
during the edition. If you have two charts and edit one, selecting the
second while editing the first will replace the second chart by a copy
of the first.

Attached patch fixes that in abiword. I'm waiting for comments before
commiting, even if I am quite confident it should not break anything (I
have also a patch for abigochart, but this one is quite trivial).

Cheers,
Happy new year

Jean