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
merge in matt's memoize changes
Merge remote-tracking branch 'remotes/origin/master' into tsmemo