By default it detects file size by fseek()'ing to its end and ftell()'ing
current position, and these functions take `long offset' as an argument.
It is sufficient on 64-bit architectures where sizeof(long) is 8, but not
so on 32-bit ones where it is 4.
Make it work everywhere by building with -DUSE_FTELLO so it uses fseeko(3)
and ftello(3) functions which take `off_t offset'.
Tested on: i386, powerpc
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