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/restore.c

@@ -522,6 +522,7 @@ unsigned int *stuckid, *steedid;	/* STEED */
 	struct sysflag newgamesysflags;
 #endif
 	struct obj *otmp, *tmp_bc;
+	char timebuf[15];
 	int uid;
 
 	mread(fd, (genericptr_t) &uid, sizeof uid);
@@ -565,6 +566,9 @@ unsigned int *stuckid, *steedid;	/* STEED */
 	amii_setpens(amii_numcolors);	/* use colors from save file */
 #endif
 	mread(fd, (genericptr_t) &u, sizeof(struct you));
+	mread(fd, (genericptr_t) timebuf, 14);
+	ubirthday = time_from_yyyymmddhhmmss(timebuf);
+
 	set_uasmon();
 #ifdef CLIPPING
 	cliparound(u.ux, u.uy);