[9fans] Fix to tm2sec().

[Dan Cross <cross@math.psu.edu>]

I fixed a bug in tm2sec() where it didn't take into account tm->yday.
Now, if tm->yday is nonzero, it uses that instead of accumulating
seconds based on month and day in month.  A patch in diff -e format
follows.

btw- The handling of tm->year seems suboptimal to me; shouldn't this be
the 4 digit year, instead of the current year - 1900?  I realize that
on Unix, (struct tm *)->tm_year is years since 1900, but this isn't
Unix, and it just strikes me as goofy.

	- Dan C.

term% diff -e /n/sources/plan9/sys/src/libc/9sys/tm2sec.c tm2sec.c
76,79c
		/*
		 * secs in last month
		 */
		secs += (tm->mday-1) * SEC2DAY;
	}
.
69,74c
	if (tm->yday != 0)
		secs += (tm->yday - 1) * SEC2DAY;
	else {
		/*
		 *  seconds per month
		 */
		d2m = yrsize(year);
		for(i = 0; i < tm->mon; i++)
			secs += d2m[i+1] * SEC2DAY;
.
term% pwd
/sys/src/libc/9sys
term%