add mexta field to simplify detection of overwrite

Because this invalidates existing save and bones files,
an increment of EDITLEVEL will accompany this.

include/mextra.h

@@ -75,6 +75,7 @@ struct fakecorridor {
 };
 
 struct egd {
+    unsigned parentmid;   /* make clobber-detection possible */
     int fcbeg, fcend;     /* fcend: first unused pos */
     int vroom;            /* room number of the vault */
     coordxy gdx, gdy;     /* goal of guard's walk */
@@ -92,6 +93,7 @@ struct egd {
  **     formerly epri.h -- temple priest extension
  */
 struct epri {
+    unsigned parentmid;   /* make clobber-detection possible */
     aligntyp shralign; /* alignment of priest's shrine */
     schar shroom;      /* index in rooms */
     coord shrpos;      /* position of shrine */
@@ -118,6 +120,7 @@ struct bill_x {
 };
 
 struct eshk {
+    unsigned parentmid;   /* make clobber-detection possible */
     long robbed;          /* amount stolen by most recent customer */
     long credit;          /* amount credited to customer */
     long debit;           /* amount of debt for using unpaid items */
@@ -145,6 +148,7 @@ struct eshk {
  **     formerly emin.h -- minion extension
  */
 struct emin {
+    unsigned parentmid;   /* make clobber-detection possible */
     aligntyp min_align; /* alignment of minion */
     boolean renegade;   /* hostile co-aligned priest or Angel */
 };
@@ -165,6 +169,7 @@ enum dogfood_types {
 };
 
 struct edog {
+    unsigned parentmid;       /* make clobber-detection possible */
     long droptime;            /* moment dog dropped object */
     unsigned dropdist;        /* dist of dropped obj from @ */
     int apport;               /* amount of training */