More 64-bit fixes

SystemInfo.pm:
    Use sizeof for $OSVERSION.
    Update struct used by GetSystemInfo (UINT_PTR is supported).
    Update comment about $proc_type. 
test.pl:
    Fix ProcessorInfo test (return value isn't always numeric). 
example.pl:
    Add example.pl script.

I've tested it on Strawberry Perl 5.16.2.1 64-bit using Win32::API 0.65 and 0.75 and on Strawberry Perl 5.16.2.1 32-bit using Win32::API 0.75 (0.65 would not install).