Ripped from FormEncode and strainer just to support Pythons 2 and 3.
Intended for use in your webapp test suites.
Example usage::
>>> from sieve.operators import eq_xml, in_xml
>>> a = "<foo><bar>Value</bar></foo>"
>>> b = """
... <foo>
... <bar>
... Value
... </bar>
... </foo>
... """
>>> eq_xml(a, b)
True
>>> c = "<html><body><foo><bar>Value</bar></foo></body></html"
>>> in_xml(a, c) # 'needle' in a 'haystack'
True
