to set_split_vfo/get_split_vfo, and take an extra transmit vfo arg.
Ascending compatibility is retained at the API frontend level.
NOTE: only function name has changed. The backends do not implement
necessarily the new semantic (the extra tx vfo is just ignored).
git-svn-id: https://hamlib.svn.sourceforge.net/svnroot/hamlib/trunk@1425 7ae35d74-ebe9-4afe-98af-79ac388436b8