Fixes bug 603724. Explicitly provide a buffer for setvbuf() and setbuf() in PyFile_SetBufSize(). The C99 standard allows (and glibc 2.2.5 implements) setvbuf() to ignore the size argument when the buffer argument is NULL. Tested against Python 2.3 on Red Hat 7.3 with glibc 2.2.5-43.