Issue #10740: sqlite3 no longer implicitly commit an open transaction before DDL statements

This commit contains the following commits from ghaering/pysqlite:

* f254c53494
* 796b3afe38
* cae87ee686
* 3567b31bb5

With the following additions:

* Fixed a refcount error
* Fixed a compiler warning
* Made the string comparison a little more robust
* Added a whatsnew entry

Modules/_sqlite/statement.h

@@ -38,6 +38,7 @@ typedef struct
     sqlite3_stmt* st;
     PyObject* sql;
     int in_use;
+    int is_ddl;
     PyObject* in_weakreflist; /* List of weak references */
 } pysqlite_Statement;