pydal for_update on sqlite

[Eric]

I'm using pydal revision 20191227.1 installed via pip.

Trying to use "for_update" in select on sqlite database results in an exception

    sqlite3.OperationalError: near "FOR": syntax error

The adapter for sqlite does have special handling for "for_update", but it looks like pydal is adding " FOR UPDATE" to the select statement for all databases including sqlite, which causes the problem.

Related to this:

https://groups.google.com/forum/#!topic/web2py/0dD6SmKPuFU