remove spurious SET_LINENO from com_list_for and com_list_if. All they do

remove spurious SET_LINENO from com_list_for and com_list_if.  All they do
is slow things down unnecessarily and make tracing much more verbose.
Something like

    def f(n):
	return [i for i in range(n) if i%2]

should have at most two SET_LINENO instructions, not four.  When tracing,
the current line number should be printed once, not 2*n+1 times.