barbarically thread-safe memoize
When building with ACL2_MT_MEMO=1 and ACL2_PAR=p, turn multithreading
memoization on by default, since that's safer.

Insert limit on the number of "ignoring time increment" messages that
will be printed, in case of horribly incorrect timings.

Expand memoize tests with some multithreaded tests.  Kind of a mess
because I was debugging issue 264.
Merge remote-tracking branch 'remotes/origin/master' into tsmemo
simplify multithreaded memoize build stuff
patch up memo tests to work on acl2(hp)
update memoize tests with new timing info
tweaks to memoize
Merge remote-tracking branch 'remotes/origin/master' into tsmemo
tweak vl model command to write out .ver files as well.
add read-file-as-string function to std-io
Merge remote-tracking branch 'remotes/origin/master' into tsmemo
Incorporated mod from J (with further mods to some books) for untranslating car-cdr nests.

Quoting :doc note-7-0:

  Nests of [car] and [cdr] calls are now printed (``untranslated'')
  differently. The old method availed itself of all 28 of the car-cdr
  macros. The new method only introduces 6 of them: cadr, caddr,
  cadddr, cddr, cdddr, cddddr. This code never introduces such macros
  as caar or cddaar, preferring cars and cdrs when necessary. Lisp
  programmers tend to recognize cadr, caddr, and cadddr as the
  accessors for the 1st, 2nd, and 3rd (0-based) elements of a list.
  See community book books/system/untranslate-car-cdr.lisp for
  further discussion and a correctness proof.
Syched doc.lisp
merge in matt's memoize changes
Merge remote-tracking branch 'remotes/origin/master' into tsmemo
VL: add support for `define macros with arguments

This turns out to be pretty hideous.  Added a few systests to try
to test it.  Started toward extending VL systests to VCS instead of
just NCV, but that's probably not working yet.
fix bug with memoize tests
Updated SINCE in purity script to avoid irrelevant log issue.