test(scope_spec) allows destroying a  with a removal function
feat(scope.js)  returns a removal function
test(scope_spec) allows destroying a  during digest
feat(scope.js)  destroys itself during digest
test(scope_spec) allows a watch to destroy another during a digest
refactor(scope.js) eliminate the short-circuiting optimization on watch removal
test(scope_spec) allows destroying several  during digest
refactor(scope.js) 22530digestOnce checks to see if the given watcher is valid before executing
refactor(scope_spce) restructure describe blocks
test(scope_spec) child scope inherits the parent's properties
test(scope_spec) does not cause a parent to inherit its properties
test(scope_spec) inherits the parent's properties whenever they are defined
test(scope_spec) can watch a property on the parent scope