Fix a bug involving
+ frequent changes in and out of WAL mode and
+ VACUUM that could (in theory) cause database corruption.
+
Enhance the sqlite3_trace() mechanism so that nested SQL statements
+ such as might be generated by virtual tables are shown but are shown
+ in comments and without parameter expansion. This
+ greatly improves tracing output when using the FTS3/4 and/or RTREE
+ virtual tables.
+
Change the xFileControl() methods on all built-in VFSes to return
+ SQLITE_NOTFOUND instead of SQLITE_ERROR for an unrecognized
+ operation code.
+