r.terraflow limited to 32bit temp files in WinGrass

[hamish]

Hi,

moving this out of the noise of #1006 so we can close that one asap.

part of the work-around for the #1006 r.terraflow on WinGrass fix replaces stat() with ftell(), as stat() on Windows gives undefined results if the file is still open.

The ftell() solution is not 32bit safe though, so it awaits a backport of G_ftell() [or even better off_t G_filesize()] in some later release.

This does not affect the UNIX side of things, the ftell() is within a #ifdef.

Hamish