fixed IndentationError

this got pulled in in #15

IndentationError: unindent does not match any outer indentation level
Made library more testable by allowing PAYPAL_TEST to be changed at runtime in tests
Added tests for payments form
More robust test for form
QueryDict is immutable. Create a copy before trying to change it.
Fixed crasher with Python 3 and IPN postbacks
Corrected type of PayPalStandardBase.query

Thanks to hongquan for the catch
fixes markup for signal documentation
Merge pull request #21 from codingjoe/patch-1

fixes markup for signal documentation
Merge pull request #1 from spookylukey/master

merging master changes