Back out the changes to _uClibc_fread and loop in fread() if incomplete, to

Back out the changes to _uClibc_fread and loop in fread() if incomplete, to
avoid problems with fgets on tty streams.  I actually did some testing this
time.  ;-)
Note: there is a difference in behavior between glibc and uClibc here
regarding fread() on a tty stream.  glibc's fread() seems to return after
reading all _available_ data even if not at end-of-file, while uClibc's
fread() continues reading until all requested or eof or error.  The latter
behavior seems correct w.r.t. the standards.