Add Implicit Async Functions (#3757)

* changed jison acceptable versions

* added await support

* wrong function bug fix

* added tests for async/await

* invalid to have await, yield(from) in same function

* changed error handling and tests

* bug fix

* made error handling test more rigorous

* consolidated harmony test files

* added async constructor support and tests

* removed .orig files

* Fixed browser testing issue

* Minor cleanup

* Async test-suite and Cake support, simplified/removed funky tests

* Skip async/await tests when not supported in runtime

* cleanup

* Replaced polyfill with native JS async/await

* Oops

* Make 'async' reserved word

* Remove all async polyfills

* fix merge conflict

* make async testing opt-in

* restore test, remove confusing polyfill language

* Revert changes to test runners

* Only run async tests where async/await is supported (Node 7+ with --harmony, for now)

* remove 'async' from JS reserved words

* The async tests should use their own special async-capable version of `global.test`, which is only loaded for the async tests and only loaded by async-capable environments

* Reverting rename of `async`, it’s not a reserved word so there’s no longer a need for this change

* async test refactoring and additions

* oops

* sync

* better error reporting for `await`

* more stuff geoffrey wants

* fixed litcoffee tests

* change test title

Cakefile

@@ -228,10 +228,14 @@ task 'bench', 'quick benchmark of compilation time', ->
 # Run the CoffeeScript test suite.
 runTests = (CoffeeScript) ->
   CoffeeScript.register()
-  startTime   = Date.now()
-  currentFile = null
-  passedTests = 0
-  failures    = []
+  startTime = Date.now()
+
+  # These are attached to `global` so that they’re accessible from within
+  # `test/async.coffee`, which has an async-capable version of
+  # `global.test`.
+  global.currentFile = null
+  global.passedTests = 0
+  global.failures    = []
 
   global[name] = func for name, func of require 'assert'
 
@@ -288,10 +292,10 @@ runTests = (CoffeeScript) ->
   # Run every test in the `test` folder, recording failures.
   files = fs.readdirSync 'test'
 
-  # Ignore generators test file if generators are not available
-  generatorsAreAvailable = '--harmony' in process.execArgv or
-    '--harmony-generators' in process.execArgv
-  files.splice files.indexOf('generators.coffee'), 1 if not generatorsAreAvailable
+  # Ignore async test file if async/await is not available
+  asyncSupported = parseInt(process.versions.node.split('.')[0]) >= 7 and
+    ('--harmony' in process.execArgv or '--harmony-async-await' in process.execArgv)
+  files.splice files.indexOf('async.coffee'), 1 unless asyncSupported
 
   for file in files when helpers.isCoffee file
     literate = helpers.isLiterate file