Demonstrate git-show is broken with ranges

The logic of git-show has remained largely unchanged since around
5d7eeee (git-show: grok blobs, trees and tags, too, 2006-12-14): start
a revision walker with no_walk=1, look at its pending objects and
handle them one-by-one.  For commits, this means stuffing them into a
new queue all alone, and running the walker.

Then Linus's f222abd (Make 'git show' more useful, 2009-07-13) came
along and set no_walk=0 whenever the user specifies a range.  Which
appears to work fine, until you actually prod it hard enough, as the
preceding commit shows: UNINTERESTING commits will be marked as such,
but not walked further to propagate the marks.

Demonstrate this with the main tests of this patch: 'showing a range
walks (Y shape)'.  The Y shape of history ensures that propagating the
UNINTERESTING marks is necessary to correctly exclude the main1
commit.  The only example I could find actually requires that the
negative revisions are listed later, and in this scenario a dotted
range actually works.  However, it is easy to find examples in git.git
where a dotted range is wrong, e.g.

  $ git show v1.7.0..v1.7.1 | grep ^commit | wc -l
  1297
  $ git rev-list v1.7.0..v1.7.1 | wc -l
  702

While there, also test a few other things that are not covered so far:
the -N way of triggering a range (added in 5853cae, DWIM 'git show -5'
to 'git show --do-walk -5', 2010-06-01), and the interactions of tags,
commits and ranges.

Pointed out by Dr_Memory on #git.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

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