BUG: fix large file support on 32 bit systems

On linux large file support must be enabled and ftello used to avoid
overflows. The result must not be converted to a size_t, but a long
long.
BUG: fix npy_PyFile_Dup error handling

no caller deals with the -1.
TST: run 32 bit test with python3
TST: run slow chroot test earlier for better load balancing
MAINT: add a configure check for ftello and fseeko

Works on Ubuntu/Debian, might require lfs macros on some platforms to
succeed, but its also defined by Python.h so it should mostly work.
TST: document reason for truncate instead of seek past end
Merge pull request #4187 from juliantaylor/large-file-fix

BUG: Fix large file support on 32 bit