AND may not do the right thing in SICL LOOP

[robert-strandh]

Example: (loop for n from 1 to 3 and x = n collect (list n x))
return ((1 1) (2 2) (3 3)), but the use of and may mean
that N is NIL the first time around, so this is the wrong answer if so.

[skempf]

There is one test in the ANSI suite for using the and iteration clause grouping (reference loop.17.21), which happens to be commented out in Code/Loop/Test/loop17.lisp.

As an aside, test loop.17.20 is also commented out, but sicl-loop passes this test.