SF bug 538827:  Python open w/ MSVC6: bad error msgs. open_the_file:  Some (not all) flavors of Windows set errno to EINVAL when passed a syntactically invalid filename.  Python turned that into an incomprehensible complaint about the mode string.  Fixed by special-casing MSVC.
SF bug 538827:  Python open w/ MSVC6: bad error msgs.
open_the_file:  Some (not all) flavors of Windows set errno to EINVAL
when passed a syntactically invalid filename.  Python turned that into an
incomprehensible complaint about the mode string.  Fixed by special-casing
MSVC.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator