Merge the scheme-parse-refactor changes into trunk: (1) added

sqlite3SchemaMutexHeld() asserts, (2) Use -1 instead of 0 to mean
"all" in sqlite3ResetInternalSchema(), and other cosmetic changes.

FossilOrigin-Name: 5db4511d8a77b74be3503a7c34257ef6b07541f5

src/fkey.c

@@ -1154,6 +1154,7 @@ void sqlite3FkDelete(sqlite3 *db, Table *pTab){
   FKey *pFKey;                    /* Iterator variable */
   FKey *pNext;                    /* Copy of pFKey->pNextFrom */
 
+  assert( db==0 || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
   for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
 
     /* Remove the FK from the fkeyHash hash table. */