test(scope_spec) ends the digest when the last watch is clean
fix(scope_spec) change digest() to ()
feat(scope.js) digest ends  when the last watch is clean
test(scope_spec) scope does not end the digest so that new watches are not run
fix(scope_spec) change digest() to ()
feat(scope.js) scope does not end the digest so that new watches are not run
test(scope_spec)  compares based on value if enabled
feat(scope.js) add 6185areEqual function and  compares based on value if enabled
test(scope_spec)  correctly handles NaNs
feat(scope)  correctly handles NaNs