Warn when pure expressions are used in sink context

even if the arguments are not constant, or the expression warns.
By explicit request from TimToady++ at
http://irclog.perlgeek.de/perl6/2013-02-18#i_6469204
awesomify sink context warning text
turn LTA error for coercive type declarations into NYI.
update ChangeLog
[release] bump NQP revision
[release] bump VERSION
[release] Add a new release announcement
Update the release guide
Some formatting updates to 2013.02 announcement.
[docs] update the download step in the release guide
interpolation of e.g. regexes in arrays in regexes
bump VERSION and NQP_REVISION to 2013.02.1

this gets us non-broken native call suport
force regexes in array to match at pos 0 only
switch type name gistification from Type() to (Type)
Fix an incorrect package name.

Not sure how this ever worked before; fixes the failing tests.
bump nqp revision
Merge remote-tracking branch 'origin/agressive-sink-warnings' into nom
Tweak an error message; TimToady++.
[docs] release announcements in markdown

* update release_guide
* add a template for the announcement for next month, provided by uvtc++

the format we use is quite close to markdown already, and writing it
in proper markdown makes them display nicely on github, and easier to
translate to HTML
Updates to work with latest HLL::Compiler.

Makes things a little cleaner, by not coupling to the backend stages
at all. Should cut out one bit of what the --target=pbc support had
to update.