[Libreoffice] SmNodeToTextVisitor Fixes

[Luke Dixon]

Hello again,

Sorry, forgot something.
> 3. Some of the subs & sups seemed to need extra brackets when used
with
> an operator node (for example int or sum).
4. Matrices with blank elements seem to cause problems so I added more
brackets (supposed to be removing them :( ).

Also, I've made the code used to find these into cppunit tests. I took
all the formula commands from:
http://wiki.services.openoffice.org/wiki/Template:Math_commands_reference

This page is licensed with the Creative Common Attribution 3.0 license
(CC-BY), so I put a note in the code with all the contributors names
(Hopefully that covers it).

What the code does is parses the formula command, runs the
NodeToTextVisitor on it, then parses it again, then visits again.
It occurred to me that the NodeToTextVisitor should output the same text
both times.

It was quite fun writing this and learning about the different string
types that are used and working out how to do this without putting
printf all over the place.
I didn't see any of the other tests doing like this with the
assertion_traits template and CPPUNIT_ASSERT_EQUAL_MESSAGE, so I hope I
haven't gone too far.

Regards,
Luke