Use wxINT32_MAX instead of LONG_MAX as the upper bound in wxDateTime::IsInStdRange().

Use wxINT32_MAX instead of LONG_MAX as the upper bound in wxDateTime::IsInStdRange().

Under Debian Linux 64 bit time_t is 64 bit long but libc doesn't seem to handle values beyond 2^32
correctly, e.g. wrong results are returned from localtime() for them. And it would seem that platforms
where sizeof(long) > sizeof(time_t) might exist too so it seems safer to only work with 32 bit time_t
values until we can reliably detect platforms which support 64 bit ones.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61497 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775