[BZ #471] Fix imported from gnulib.

[BZ #471] Fix imported from gnulib.

	* time/mktime.c (leapyear, ydms_tm_diff): Year is of type
	long int, not int, to avoid problems when tm_year == INT_MAX
	and tm_mon > 12.
	(__mktime_intenral): Compute year using long int arithmetic,
	not int arithmetic, to avoid problems on hosts where time_t
	and long are 64 bits but int is 32.