formula unit fix test case 12070 v05 to produce message
correct formula and function operations involving xs:decimal and
xs:double arguments to promote python Decimal arguments to float
arguments.  (Python itself promotes mixtures of integer and Decimal
to Decimal.)

correct fn:insert-before and fn:remove to require integer arguments
(xs:decimal and xs:double not allowed).
provide a stringValue operation on objects returning the inner
text (but not contents of comment nodes, just their 'tail' text
nodes).  Needed because fn:data is always the inner text of mixed
content or descendant elements.
change xPath parser to match rules determining xs:decimal and
xs:double, a number with a "." and no E is a decimal, and only
with E does it become a float (xs:double).  Type promotion in
xPath arithmetic covers converting mixtures of decimal and float.
correct imports of urllib for python 2.7 conversion