Fix bug where dummy_thread was always imported

The code always import the dummy_thread module even on platforms where the real thread module is available. This caused bugs in other packages that use this import style:

try:
    from _thread import interrupt_main  # Py 3
except ImportError:
    from thread import interrupt_main  # Py 2

See  https://github.com/ipython/ipython/pull/7079
Add missing import to fix OrderedDict.clear.
Add signed support to newint_bytes
Error handling is hard
Fixed newrange equality for empty ranges and irrelevant stop differences
Fixed newrange slicing
Added test_range.py suite
Merge pull request #128 from beckjake/newint_bytes

Add handling for signed integers to newint.to_bytes and newint.from_bytes
Merge pull request #129 from bradmwalker/range-fixes

newrange equality and slicing fixed
Uncomment some newint.to_bytes tests
Merge pull request #125 from QuLogic/OrderedDict-clear

Add missing import to fix OrderedDict.clear.
Merge pull request #124 from melund/master

Fix bug where dummy_thread was always imported
Remove import of dummy_thread from _thread module (issue #124)
Add authors of recent patches to credits.rst
newrange: added attr read-only properties
Update What's New page for v0.14.3
simplified range_iterator (renamed for consistency)
newrange: fixed slices on empty ranges
simplified newrange.__reversed__ and corrected return type
Docs: tweak What's New page
Merge pull request #130 from bradmwalker/more-range-work

newrange: read-only getters, empty range slice fix,  and refactoring
Docs: mention PR #130 in What's New page