Fix copy-and-paste bug.
Fix copy-and-paste bug.

Our assumption that history_convert is always invoked from within
copy_selection is invalid.  Copying from xtickertape and pasting into
firefox-3.5 (at least into the Google language tools text area with
Ubuntu-9.04) invokes copy_select at copy time and history_convert when
the paste is done.

tphelps/xtickertape,tphelps/xtickertape,tphelps/xtickertape,epronk/xtickertape,epronk/xtickertape