Only treat Python Lists as array dimensions.

Only treat Python Lists as array dimensions.

Instead of treating all python sequence types as array dimensions, except
for tuples and various kinds of strings, only treat Python lists as
dimensions. The PyBytes_Check() function used previously is only available
on Python 2.6 and newer, and it was a bit fiddly anyway. The list of
exceptions would require adjustment if Python got a new kind of a sequence
similar to bytes/unicodes/strings, so only checking for Lists seems more
future-proof. The documentation only mentioned using Lists, so this is
closer to what was documented, anyway.

This should fix the buildfarm failures on systems building with Python 2.5,
although I don't have Python 2.5 installed myself to test with.