Stop relying on the message text of ZeroDivisionError in tests.

The test for broken_repr relied on the message text of
ZeroDivisionError, which is different on pypy (just "integer
division", not "integer division or modulo"). This causes a test
failure. Fix this by explicitly raising an exception with a message we
provide.
local: add swapped operands support for LocalProxy
fix strings tests
Fix relying on order of unordered types

Modified version of #234

All changed tests have in common that they assert a specific ordering of
an unordered data structure (dict or set). The assertions have been made
more liberal with respect to the order of entries.

Command used for finding failures of this kind:
for i in `seq 100`; do echo PYTHONHASHSEED=$i;
PYTHONHASHSEED=$i $PYTHON run-tests.py || break; done
Merge pull request #193 from marienz/tweak-test-for-pypy

Stop relying on the message text of ZeroDivisionError in tests.
Fixed #271
Merge pull request #273 from untitaker/request_files

Fixed #271
Added changelog entry
Merge pull request #268 from simonz05/local-operands

local: add swapped operands support for LocalProxy
Added changelog entry for local proxy changes
Merge pull request #269 from untitaker/ordering_assumptions

Fix relying on order of unordered types
Added a hook to override the converter selection in the routing system