Use "hpss" tag for smart server bugs

[Andrew Bennetts]

Hi all,

I've started adding the "hpss" tag to bugs relating to the smart server.  Please
add this to any bugs you see or file about smart server related issues, it'll
make it easier for me (and other interested developers) to find.  Once the
current hpss branch lands, I expect to spend some time going through these bugs
and fixing the glitches they report.  Of course, you don't have to wait for me
if you want to fix them today ;)

("hpss" stands for "High-Performance Smart Server", for those who didn't already
know.)

I've updated http://bazaar-vcs.org/BugGuidelines to have a "Tags" section, and
included the "hpss" tag in it.

-Andrew.