RkLeft - move the current clause to the clause to its left
#include <canna/RK.h>
int RkLeft(cxnum)
int cxnum;
RkLeft moves the current clause to the clause to its left, or to the
last clause if the current clause is 0.
If successful, this function moves the current clause in the context
and returns the current clause number after the move. It returns 0,
without doing anything, if it has been run in a nonconversion mode
context.