Closing a few JIRA fomula comments

Some of the JIRA formula comments that were technically open should really be closed.

To save us some time tomorrow, I'm trying to close just a few of the "most obvious" ones that we've previously discussed, but for various reasons are open in the new JIRA list.  Of course, if you disagree, please let us know and we'll re-open.  Here's what I've closed:

Unit system tracking
http://tools.oasis-open.org/issues/browse/OFFICE-550
No, we're not adding unit system tracking (at least, not this round!)

Comment on test case for LEFT()
http://tools.oasis-open.org/issues/browse/OFFICE-358
No, the test case is correct. Length of -0.1 is <0, and thus wrong.

--- David A. Wheeler