Represent a subfield expression as a variant of a function call

Represent a subfield expression as a variant of a function call
expression, rather than a function call in its own right.

1. Eliminate 'xfld' as a valid value for query.expression.type.

2. Eliminate the query.expr_xfld view.

3. Expand the query.expr_xfunc view to include the column_name column.

M    Open-ILS/src/sql/Pg/002.schema.config.sql
M    Open-ILS/src/sql/Pg/008.schema.query.sql
A    Open-ILS/src/sql/Pg/upgrade/0322.schema.query.no-xfld-expr.sql
M    Open-ILS/examples/fm_IDL.xml

git-svn-id: svn://svn.open-ils.org/ILS/trunk@16824 dcc99617-32d9-48b4-a31d-7c20da2025e4