cpptrad.c (_cpp_scan_out_logical_line): Improve test for whether directive begins at the beginning of a line.

	* cpptrad.c (_cpp_scan_out_logical_line): Improve test for
	whether directive begins at the beginning of a line.

	(testsuite)
	* gcc.dg/cpp/trad/xwin1.c: New test case.

From-SVN: r73740