exclude PyLong optimisation for arithmetic operators in Py2.7 as it's actually unlikely that we'd encounter C long sized PyLong objects in Py2.x (which has the 'int' type for that)

fix crash in MarkParallelAssignments transform when it hits a type inferred TypedExprNode that lacks pos/subexprs

extend PyLong optimisations to everything that fits into a C long (Py2.7 uses 15 bit digits even on 64 bit platforms, i.e. C long covers 4 digits)

--HG--
extra : transplant_source : %0F%A1%10%B6%0D%82%1D%A3%1A%3A%B1%94%10%E9%D6%ADh%29Ni

--HG--
extra : transplant_source : %A5%88%3ES%0C%2B%5Bh%BC%83%8E%F3%E8%11%2A%0A%B4j%D5%29

Fix document error "*.pyx" -> ["*.pyx"]

Document update cythonmagic -> Cython

let CPython do its own PyLong->PyFloat rounding for large numbers in float +/- operator optimisation

--HG--
extra : amend_source : 7d848b95b73159432b1eb94e238006dda0bd6e32