Update test262 snapshot
Tolerate case change in test262 output

The test262 upstream changed "Failed tests" to "Failed Tests" which broke
the python parsing of errors.
Switch to stable es5-tests branch of test262

The master of test262 seems to have too much activity and right now some
tests are buggy.
Remove ES6 known issues, es5-tests doesn't need it
Merge branch 'use-test262-es5-tests-branch'

Move to using the "es5-tests" branch of test262.