HHVM (3.2.0+) for cedar-14
warn on strict version selectors
remove HHVM 3.1.0 due to missing packages upstream
compile: cache downloaded files in $CACHE_DIR
enable calendar and FTP PHP extensions, shared
update ext/mongo to 1.5.5
update ext/newrelic to 4.11.0.63
defend against invalid composer.phars
PHP/5.6.0RC4
Merge branch 'feature/cache-downloads' into develop

* feature/cache-downloads:
  compile: cache downloaded files in $CACHE_DIR

Conflicts:
	bin/compile