Eliminate references to various list filters in favor of SRFI-1.

Eliminate references to various list filters in favor of SRFI-1.

One unfortunate development is that somewhere in the compiler is some code that
depends on the result of a filtering option being newly allocated, while FILTER
shares the tail of the input list when it can.  I modified FILTER to stop doing
that, because it wasn't obvious which of the modified calls in the compiler was
causing the problem.