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.

include/decl.h

@@ -251,6 +251,7 @@ E NEARDATA anything zeroany;		/* init'd and defined in decl.c */
 
 #include "you.h"
 E NEARDATA struct you u;
+E NEARDATA time_t ubirthday;
 
 #include "onames.h"
 #ifndef PM_H		/* (pm.h has already been included via youprop.h) */