Return t if L1, a list specification of a version, is lower or equal to L2.
Note that integer list (1) is equal to (1 0), (1 0 0), (1 0 0 0),
etc. That is, the trailing zeroes are insignificant. Also, integer
list (1) is greater than (1 -1) which is greater than (1 -2)
which is greater than (1 -3).