remove time_t from struct you (trunk only)

There was an issue reported where save files between different
versions of a manufacturer's compiler were incompatible because the time_t
ubirthday field was changed from 32 bits to 64 bits.

32 bit time_t implementations will break at 19:14:07 on  January 18, 2038.
64 bit time_t implementations will break at 23:59:59 on December 31, 3000.

This removes the dependency on the size of time_t from the save file.
The ubirthday field is no longer embedded in struct you.
This also adds two general purpose routines to hacklib.c, one to convert a time
value to a 14 character char representation and the other to convert that
back to time_t. Those are used by the save/restore routines.

This is a savefile breaking change, so editlevel in patchlevel.h was
incremented.

src/read.c

@@ -104,7 +104,7 @@ doread()
 	    if (erosion)
 		wipeout_text(buf,
 			(int)(strlen(buf) * erosion / (2*MAX_ERODE)),
-			     scroll->o_id ^ (unsigned)u.ubirthday);
+			     scroll->o_id ^ (unsigned)ubirthday);
 	    pline("\"%s\"", buf);
 	    return 1;
 #endif	/* TOURIST */