add some unit tests

add test to repro #114
fix issue #114
factor out PercentFormat function
new fn write; start factoring summary output
fix tests to match
consolidate "Failed Tests" message
add test for successful run
consolidate all_succeeded message
consolidate summary line
consolidate ntests
failing negative tests
squeeze whitespace
Merge pull request #115 from smikes/issue-114-logname

test262.py crashes when --logfile due to reference to absent attribute 'logfile'
es6 compatability updates

See also: https://github.com/tc39/test262/pull/29