Implement squish() and .squish(), as per S32/Containers
Streamline "uniq" and "squish", suggested by jnthn++

See http://irclog.perlgeek.de/perl6/2013-07-03#i_7284148
[docs/release_guide.pod] add moritz and me for Aug/Sep
Restore "uniq" to unstreamlined form, it messes up odd things
Optimize lexical out of hot loop in "uniq"

And I've now given up on using grep{} in uniq(), the tests succeeed, but strange
unrelated things change, like giving the wrong error message:
$ perl6 -e 'Module.new'
===SORRY!===
Cannot assign a non-Perl 6 value to a Perl 6 container
Implement CallFrame.

Seems line number is off by one, but works otherwise. Unbusts 3 test
files, two of which pass in full, one with one failure.
Add some checks for dumbo's trying to unshift/push infinite lists