introduce int cells to avoid object allocation
intcells are also closure cells, but with possibly only an intvalue
nits
Merge remote-tracking branch 'origin/master' into tim/intcells
update test
Merge remote-tracking branch 'origin/master' into tim/intcells
fix trace
Add libffi-dev to the list of dependencies
Merge pull request #392 from Alexis-D/master

Add libffi-dev requirement in docs/getting-started.txt
Merge pull request #342 from topazproject/tim/intcells

Introduce int cells to avoid object allocation