'springboard' selftest passes.
bump a test timeout
put some try/catch blocks around maybeDownloadPackageForArchitectures. Not sure that this is the best plan?
more error handling and reporting on package changes & downloads
better error handling
new dev bundle

Changes:

- Drop keypress; it hasn't been used since we rewrote prompts to use
  built-in readline

- Use a slightly newer version of npm, to avoid strange thing where it
  creates ~/tmp

- Drop node-aes-gcm and bcrypt: we now can support cross-platform
  package deploys directly!  (A follow-up commit will add them
  to the corresponding packages.)

- Drop heapdump: it was only there for convenience, and now can also be
  added via a package

- upddate some comments
ignore build IDs in constraint solver
stop mongo-livedata from being non-portable

it is way too hard to get a non-portable package to work both from
uniload (which can't depend on non-core packages) and with meteor deploy
from checkout on mac (which basically requires a non-core package to
have the non-portability in it)
wrapper checkpoint
can't override npm version

bump dev bundle again

sigh.  in trying to work around a silly bug (npm creates ~/tmp), it
turns out that you can't actually install npm like that --- because it
reverts the hack done by 'make install PORTABLE=1' to make npm find node
properly (because that hack literally rewrites a file in the npm module)
more error for the thing we're seeing
packages/non-core/foo is not in core