Merge changes from the trunk into the threads branch.

FossilOrigin-Name: 416cb091267de91b9cadee9f7453b8627570b7d3

src/vdbesort.c

@@ -637,7 +637,6 @@ static int vdbePmaReaderSeek(
       rc = sqlite3OsRead(
           pReadr->pFile, &pReadr->aBuffer[iBuf], nRead, pReadr->iReadOff
       );
-      assert( rc!=SQLITE_IOERR_SHORT_READ );
     }
   }