1.0.46.16: death to "in: LAMBDA NIL" in compiler messages

1.0.46.16: death to "in: LAMBDA NIL" in compiler messages

 The LAMBDA NIL was 99% of the time the lambda introduced by
 %SIMPLE-EVAL-IN-LEXENV -- in other words totally uninteresting.

 Have EVAL save original form, and use that to name the lambda
 introduced in %SIMPLE-EVAL-IN-LEXENV:

   `(NAMED-LAMBDA (EVAL ,SOURCE-CONTEXT) ...)

 Finally, DEFINE-SOURCE-CONTEXT for NAMED-LAMBDA that understands the
 source context stashed into the name by %SIMPLE-EVAL-IN-LEXENV.

 Additionally, in case there is a legitimate (LAMBDA () ...) form the
 compiler wants to complain about, make sure it is printed as LAMBDA (),
 not LAMBDA NIL.