JDBC index metadata filter_condition

I'm investigating a Java based schema designer tool which uses the JDBC
metadata API for most of its information gathering. I notice that the
filter_condition field  returned in the getIndexInfo() method's
resultset is always null. It seems straightforward to fix this (see
attached patch)

I've specified 7.4 as the earliest server version that will try to
populate this field - even tho it looks like 7.3 might work (do we care
about 7.3 and earlier?)

regards

Mark