Fixes to without-interrupts (GCL only), :doc sys-call, two loop index types in memoize-raw.lisp.  Renamed defdata-regression.lisp to .lsp.

Fixed gcl-only bugs in without-interrupts.

Updated :doc sys-call to clarify (as per IRC channel discussion) that
one cannot expect shell expansion of arguments.

Improved types from integer to mfixnum on a couple of loop indices in
memoize-raw.lisp.

Renamed a books/defdata/defdata-regression.lisp to a .lsp suffix, as
suggested by Harsh (since it's not a book).

Updated doc.lisp to match books/system/doc/acl2-doc.lisp.

Changed "SINCE" date stored in bin/purity.sh to avoid bogus error (my
changes to GNUmakefile had been the same as David Rager's).