rewriteutil: allow rewriting merge commits (issue4561)
This patch simply allows rewriteutil.rewrite() to work with commits with
multiple parents (i.e. merges). That function is used in such commands as fold,
metaedit, touch, rewind.
The issue 4561 is marked as easy, the limitation is called unnecessary, no
tests fail after this change. What can go wrong.
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.