Factor all KeyInfo object allocations into a single function:

sqlite3KeyInfoAlloc().  Always allocate enough space so that 
sqlite3VdbeRecordCompare() can avoid checking boundaries and hence
run faster.

FossilOrigin-Name: 7301bedd94c8610568349953b18ff3575203e1b2

src/sqliteInt.h

@@ -1464,12 +1464,16 @@ struct FKey {
 ** An instance of the following structure is passed as the first
 ** argument to sqlite3VdbeKeyCompare and is used to control the 
 ** comparison of the two index keys.
+**
+** Note that aSortOrder[] and aColl[] have nField+1 slots.  There
+** are nField slots for the columns of an index then one extra slot
+** for the rowid at the end.
 */
 struct KeyInfo {
   sqlite3 *db;        /* The database connection */
   u8 enc;             /* Text encoding - one of the SQLITE_UTF* values */
-  u16 nField;         /* Number of entries in aColl[] */
-  u8 *aSortOrder;     /* Sort order for each column.  May be NULL */
+  u16 nField;         /* Maximum index for aColl[] and aSortOrder[] */
+  u8 *aSortOrder;     /* Sort order for each column. */
   CollSeq *aColl[1];  /* Collating sequence for each term of the key */
 };
 
@@ -3086,6 +3090,7 @@ void sqlite3MinimumFileFormat(Parse*, int, int);
 void sqlite3SchemaClear(void *);
 Schema *sqlite3SchemaGet(sqlite3 *, Btree *);
 int sqlite3SchemaToIndex(sqlite3 *db, Schema *);
+KeyInfo *sqlite3KeyInfoAlloc(sqlite3*,int);
 KeyInfo *sqlite3IndexKeyinfo(Parse *, Index *);
 int sqlite3CreateFunc(sqlite3 *, const char *, int, int, void *, 
   void (*)(sqlite3_context*,int,sqlite3_value **),