Change the name of the Index.autoIndex field to Index.idxType and provide
symbolic names for the various values of that field rather than using
magic numbers.

FossilOrigin-Name: d16e575dacc811de0f7b58a0d1cd243678dce6c5
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index bb8763c..cc3a030 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -1694,7 +1694,7 @@
   u16 nKeyCol;             /* Number of columns forming the key */
   u16 nColumn;             /* Number of columns stored in the index */
   u8 onError;              /* OE_Abort, OE_Ignore, OE_Replace, or OE_None */
-  unsigned autoIndex:2;    /* 1==UNIQUE, 2==PRIMARY KEY, 0==CREATE INDEX */
+  unsigned idxType:2;      /* 1==UNIQUE, 2==PRIMARY KEY, 0==CREATE INDEX */
   unsigned bUnordered:1;   /* Use this index for == or IN queries only */
   unsigned uniqNotNull:1;  /* True if UNIQUE and NOT NULL for all columns */
   unsigned isResized:1;    /* True if resizeIndexObject() has been called */
@@ -1708,6 +1708,16 @@
 };
 
 /*
+** Allowed values for Index.idxType
+*/
+#define SQLITE_IDXTYPE_APPDEF      0   /* Created using CREATE INDEX */
+#define SQLITE_IDXTYPE_UNIQUE      1   /* Implements a UNIQUE constraint */
+#define SQLITE_IDXTYPE_PRIMARYKEY  2   /* Is the PRIMARY KEY for the table */
+
+/* Return true if index X is a PRIMARY KEY index */
+#define IsPrimaryKeyIndex(X)  ((X)->idxType==SQLITE_IDXTYPE_PRIMARYKEY)
+
+/*
 ** Each sample stored in the sqlite_stat3 table is represented in memory 
 ** using a structure of this type.  See documentation at the top of the
 ** analyze.c source file for additional information.