File header code fix should only replace the copyright element

[sharwell]

An XML file header may contain additional elements, including the following:

1. Horizontal bars (the series of ----------------- characters)
2. A <summary> element
3. Other XML elements
4. Other text outside of XML elements

Expected behavior

When the file header code fix corrects the <copyright> element, each of these other elements should be preserved.

Actual behavior

When the file header code fix corrects the <copyright> element, the entire header is replaced (each of the items is lost).

[peteri]

Going to have a look at this as I got burnt by it today.

[peteri]

Fixed and pull request issued.