Increase the default SQLITE_MAX_SCHEMA_RETRY to 50.  Make sure that macro
covers every case where a prepared statement might need to be reprepared due
to a schema change.  The sqlite3_exec() interface now uses 
sqlite3_prepare_v2().

FossilOrigin-Name: c1d7304c80c4a6244c8a9f6fad1eebd0f339c724
diff --git a/src/vdbeblob.c b/src/vdbeblob.c
index ae77a47..2e8fd8e 100644
--- a/src/vdbeblob.c
+++ b/src/vdbeblob.c
@@ -313,7 +313,7 @@
     }
     sqlite3_bind_int64(pBlob->pStmt, 1, iRow);
     rc = blobSeekToRow(pBlob, iRow, &zErr);
-  } while( (++nAttempt)<5 && rc==SQLITE_SCHEMA );
+  } while( (++nAttempt)<SQLITE_MAX_SCHEMA_RETRY && rc==SQLITE_SCHEMA );
 
 blob_open_out:
   if( rc==SQLITE_OK && db->mallocFailed==0 ){