Fix loss of data when using the same field name in the dublincore shema and a facet schema

Steps to reproduce:

• configure "test" facet with "description" field in it's schema
• create document instance of "File" type with "dc:description" = "foo"
• add "test" facet to it with description="bar"

Expected results:

• "dc:description" == "foo"
• "test:description" == "bar"

Actual results:

• "dc:description" == "bar"
• "test:description" == "bar"