fpos.h (fpos::operator-): Don't return reference, return original, non-modified version.

2001-06-12  Benjamin Kosnik  <bkoz@redhat.com>

	* include/bits/fpos.h (fpos::operator-): Don't return reference,
	return original, non-modified version.
	(fpos::operator+): Same.
	* testsuite/27_io/fpos.cc: Add test.

[[Split portion of a mixed commit.]]

From-SVN: r43290.2