Generate a consensus sequence from a set of sequences.
This consensus sequence will be displayed at the bottom
of the window.  The base occuring most frequently down 
a column will be placed into the consensus sequence.
In the event of a tie, a question mark (``?'') will
be placed in the consensus sequence. The variable 
USE-GAP-FOR-CONSENSUS affects the way the consensus routine 
looks at gaps (``-''). If this variable is ON, gaps will
be treated as any other sequence element.  If it is OFF,
gaps will be ignored unless there are no other bases down
that column.