if-first-time not declared obsolete
documentation strings for (iter:display-iterate-clauses) complete

Move section on predicate (first-time-p) outside of gathering clauses
Various typos and some clarifications

Fix sharpL reader, add :execute to the eval-when to make (load "iterate" :compiling t) work on clisp

More precisely, FOR ON accepts dotted lists, FOR IN errors out.
As a result, iterate::*list-end-test* was eliminated.
Behaviour is now constant and does not depend on some special variable.
Note: Documentation not yet updated, pending move to Texinfo.

Set *list-end-test* to 'endp instead of 'atom, so (iter (for foo :in something-non-list)) fails instead of silently exists

Typical use is (if (first-...-p) ...)

first-iteration-p will be t in the first loop while first-time-p will
be t when first called, then nil. Hint: first-time-p is useful for
the usual comma separated list printing problem.