#3 Add "Copy as XPath" support

[Matthew L Daniel]

This patch (against HEAD) does two things:
1. Strengthens the NodePathBar's idea of the XPath of
the selected Node
2. Allows one to copy that XPath to the System
Clipboard via the JPopupMenu and the Edit menu

The produced XPath is not guaranteed to be accurate
(especially for text() paths) due to the ignorable
whitespace difference between parsers. But it'll get
you very close, in my experience.

Not a lot of testing has been done with namespace and I
_freely_ admit that the XPath syntax is ugly.

Seems like I like Pollo a lot, huh?

[Matthew L Daniel]

Patch against HEAD to enable copying XPath to System Clipboard