diffs for ctime.c for new DST rules, v7 systems

[jgy at hropus.UUCP]

> Now, to the ctime.c diffs:
> 
> The changed file will have #define NorthAm but not USA, which is
> correct for Canada. If you are in the USA, add #define USA as well.
> (The 1974-75 change didn't apply in Canada.)
> 
> (I also put in a minor speedup posted to the net a while back;
> the test of year==74||year==75 is changed to year<=75&&year>=74,
> which it a bit faster for dates between 1975 and 1987.)
> 

If you really want a speed-up make the call to 'tzset' in localtime()
dependent on a static variable not being initialized, this provides
some time savings for things like long "ls"'s etc..