tests: add some more actions to test-issue-6028, describe what's being done This patch does two things: it explains what's happening in the test file so it's easier to understand, and also it adds checks that make sure something like swapping merge parents is not accidentally breaking anything. The primary reason to touch this test file was that it was broken by a change in core's merge.graft() that erroneously swapped merge parents. Since only evolve uses merge.graft() for merge commits and there aren't any tests in core for it, let's test it here. Plus, this test case is pretty simple and these additional checks don't make it too complicated.

Doc is generated with sphinx.

You can generate the doc with:

```
make
```

# Tutorials

For updating the tutorials, you need to have the docgraph extension installed
(https://pypi.python.org/pypi/hg-docgraph).

Then run the test-topic-tutorial.t and test-tutorial.t to update the output if
needed.

You'll need the dot binary (likely installed by the graphviz package in your
package manager) in order to have graphviz graphs rendered in the html output.

Simply run make in the docs directory should takes care of the conversion of
the tutorial .t files into .rst files. Then sphinx should do the rest of the
jobs by rendering graphviz graphs.