Skip tests on python implementations without getrefcount()

PyPy is one of these.
Added test to verify copysize handling in copy_expert

Not an original psycopg2 bug but present in pure python implementation,
e.g. ctypes issue #25 and cffi issue #5.

https://github.com/mvantellingen/psycopg2-ctypes/issues/25
https://github.com/chtd/psycopg2cffi/pull/5
Added regression test for infinity parsing in dates

...and a couple of typos.
more useful error message when comparing ranges with non-ranges
raising an exception here rather than returning False causes problems with SQLAlchemy's internal state tracking
cater for comparison of subclasses
Uniform Range eq tests style
Mention the Range eq fix in the NEWS file
Merge branch 'range_eq_typerror'