* implement popen and pclose (to an extent) for NodeJS
* bring node020 back into tests.
* ah, I see what was being done here. Fix the idris for the test.
* fix test's unreachable clause warning
* fix expectation
* Add note to CHANGELOG
* small tweaks to get popen into merge-ready state.
* first pass at signal support for node backend
* change signal values to int's
* implements defaultSignal
* return -1 as expected by calling API if any error is raised by nodejs runtime
* finishes signal support for nodejs
* extract repetitive foreign import identifiers
* fix comments
* support for system command via node backend.
* Add env var set/unset
* fix env unset function
* Update libs/base/System.idr
* modify system test to cover node and chez.
* Add base tests for env get/set
I was getting a stack overflow on the tailrec002 test, caused by this
primitive being recursive. I've made it iterative. I'm no JS expert but
I've tested its behaviour against the old version.
