gcov-io.h: Add a local time stamp.

	* gcov-io.h: Add a local time stamp.
	(struct gcov_info): Add stamp field.
	(gcov_truncate): New.
	* coverage.c (read_counts_file): Skip the stamp.
	(coverage_begin_output): Write the stamp.
	(build_gcov_info): Declare and init the stamp.
	(coverage_finish): Only unlink data file, if stamp is zero.
	* gcov-dump.c (dump_file): Dump the stamp.
	* gcov.c (bbg_stamp): New.
	(release_structures): Clear bbg_stamp.
	(read_graph_file): Read stamp.
	(read_count_file): Check stamp.
	* libgcov.c (gcov_exit): Check stamp and truncate if needed.

From-SVN: r69006