make disableWriteAheadLogging method public so apps can disable WAL

music2 app has the weird situation where it embeds the jumper C++ code
and that code uses its own version of sqlite.
so, java side may want to disable WAL to make c++ code work well with java
usage of sqlite.
since WAL is made default option for all apps, this CL makes it possible for
music2 app to disable WAL.

Change-Id: I39ddbc9b4648f12b206ff3e76d30341da5955bd4