gitweb some known issues

Visit git.git gitweb page (http://repo.or.cz/w/git.git would
work fine if git.kernel.org is too busy), and click on "GIT 1.4.4-rc1"
to view the tag (not the commit).

The navigation bar has commit/commitdiff/tree with explicit h
and hb object names that point at 'master', which feels wrong.
When the tag that is displayed points at a commit, perhaps we
would want to use that commit for commit and commitdiff?  When
the tag does not point at a commit (which is admittably very
rare), probably not showing these links is the right thing to do
(if tag points at tree it might make sense to give tree,
though).

Also shortlog/log links do not say where to begin the log with,
which means start digging from HEAD.  When we display a commit
or commitdiff, we seem to give a link to start log at that
commit, so doing the same as above for shortlog/log may make
them more consistent.