workaround for common programming error involving ctime and localtime

[Paul Eggert]

The following patch lets the tz package work around
a common programming error when using ctime and localtime.

===================================================================
RCS file: RCS/localtime.c,v
retrieving revision 1994.6.1.1
retrieving revision 1994.6.1.2
diff -c -r1994.6.1.1 -r1994.6.1.2
*** localtime.c	1994/05/05 16:24:49	1994.6.1.1
--- localtime.c	1994/05/09 10:16:11	1994.6.1.2
***************
*** 1136,1142 ****
  ctime(timep)
  const time_t * const	timep;
  {
! 	return asctime(localtime(timep));
  }
  
  /*
--- 1136,1151 ----
  ctime(timep)
  const time_t * const	timep;
  {
! 	struct tm tm;
! 
! 	/*
! 	** The following is equivalent to `return asctime(localtime(timep));',
! 	** except it does not modify localtime's static storage,
! 	** and thus it works around all-too-common bugs like
! 	** `struct tm *p = localtime(&t1); puts(ctime(&t2)); return p->tm_year'.
! 	*/
! 	localsub(timep, 0L, &tm);
! 	return asctime(&tm);
  }
  
  /*