Non-zero exit code for runtests if tests fail

Known errors and testcases requiring special options don't cause a non-zero
exit code.
Makefile trivia: echo in wrong place
Merge branch 'runtests-error-exitcode'

Make runtests exit with an error code if a testcase fails without having
a known issue or special options metadata.
Ditz issue update
Test for array concat() trailing empty elements
Remove obsolete duplicate test case

`test-bi-array-proto-concat-nonstd-trailing.js` covers this case now.
Improve array concat() trailing element test case

Check that intermediate trailing non-existent elements are handled correctly,
i.e. included in the result.
Remove non-standard array concat() test

There is now a separate test for the non-standard part of array concat()
behavior, test-bi-array-proto-concat-nonstd-trailing.js.
Add DUK_USE_NONSTD_ARRAY_CONCAT_TRAILER fix
Guide doc on array concat() trailer behavior
Release note: Array.prototype.concat() behavior
Makefile: commented out option for array concat()
Merge branch 'nonstd-array-concat'

Change default behavior of Array.prototype.concat() to match (apparently
non-standard) real world behavior of at least V8, Rhino, and Spidermonkey:

When the concat result contains trailing non-existent elements, the E5.1
behavior is to not count them towards the 'length' of the concat result.
The real world behavior is to include them in the result 'length'.
Ditz issue update
Remove token end line tracking as unused
Merge branch 'remove-end-line-tracking'

Remove end line tracking from lexer tokens.  The end line information is
not used at the moment, and there doesn't seem to be a reason to use it
in the near future either.
Ditz issue update
Test case for enum corner case from test262
Update test262 known issues state

Added a few new issues from updated test262 tests.  Added all E6 tests
from test262 into "known issues" category.
Merge branch 'test262-status-update'

Update the known issues for test262 suite:

- 1 new enumeration test failed, added bug testcase for it

- 1 new property setter test failed, due to Duktape's extra setter argument
  (property name) which the test case tests for specifically

- 2 new test failures related to current 2G array limit

A lot of E6 tests have been added to test262; those were all marked "known
issues" so that they're not counted as actual errors to fix.