Add an AS parameter to Column method in collections

The AS parameter lets callers set the column alias explicitly, or avoid
a column alias entirely, rather than relying on the autogenerated
aliases.  For collections using the Column method, this alleviates the
need to pass around the returned aliases between pieces of code.
Add an AdditionalColumn method to collections

Very similar to the Column method but adds to the table's standard
columns instead of replacing them in the select.  This lets collections
easily grab the standard columns while also grabbing the result of a
function, or a column from a joined table, etc.
Merge branch 'collection-column-selection'

Conflicts:
	t/01searches.t