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).
Improved an error message for certify-book (thanks to feedback from David Rager).  Removed obsolete file p.lisp.
Improved some comments and tweaked organization in memoize-raw.lisp, through chat with J.  Defv is now defvar in non-CCL lisps (instead of defparameter).
Merge pull request #261 from ragerdl/master

3 CLs
Fixed provisional-certification bug for verify-guards+ forms and, more generally, make-event forms with :expansion? supplied.

Quoting :doc note-7-0:

  Fixed a bug in [provisional-certification] that incorrectly caused an
  error during the convert step for [verify-guards+] forms. More
  generally, this error occurred when encountering a [make-event]
  form with a non-[nil] value supplied for the :expansion? keyword.
  Thanks to David Rager for reporting this bug.
Made a few trivial :doc fixes, and brought doc.lisp up to date with books/system/doc/acl2-doc.lisp.