Prevent unquoting of query string reserved characters

[mliarakos]

Fixes #59.

In amz_cano_querystring:

• removed the initial unquote/quote steps to prevent the introduction of quoted reservered characters
• manually quote semicolons so they aren't interpreted as an alternative delimiter to ampersand by parse_qs (AWS doesn't consider them a delimiter and this was previously handled by the quote step)

This breaks the post-vanilla-query-nonunreserved test in aws_testsuite because responses auto-quotes the URL, so in test_requests_aws4auth.py:

• undo the URL auto-quoting so that the aws_testsuite URLs are passed in without modification (previously the unquote/quote steps temporarily undid the quoting)

Added test cases to cover this issue. All tests pass. including the live tests (for the endpoints that still exist).

[tedder]

sorry for the delay. this is good!