make.py --single with *.rst file unexpected behaviour.
#### Code Sample, a copy-pastable example if possible

*When in the `doc` folder:*
```
python make.py --single $(pwd)/source/development/contributing.rst
Running Sphinx v1.8.4
loading pickled environment... done
[autosummary] generating autosummary for: index.rst
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 1 source files that are out of date
updating environment: [] 0 added, 1 changed, 0 removed
reading sources... [100%] index                                                                                                                                                      
/home/max/git/pandas/doc/source/index.rst:26: WARNING: toctree contains reference to nonexisting document 'home/max/git/pandas/doc/source/development/contributing'
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] index                                                                                                                                                       
generating indices... genindex py-modindex
writing additional pages... search
copying static files... done
copying extra files... done
dumping search index in English (code: en) ... done
dumping object inventory... done
build succeeded, 1 warning.

The HTML pages are in build/html.
```
#### Problem description
Although `sphinx-build` does exit correctly, no html file corresponding to the single required file is created in the `build/html` folder. The `build/html` folder is as follows:
```
.
├── genindex.html
├── index.html
├── objects.inv
├── py-modindex.html
├── search.html
├── searchindex.js
├── _sources
│   └── index.rst.txt
└── _static
    ├── ajax-loader.gif
    ├── banklist.html
    ├── basic.css
    ├── ...
```

The page opened in the web browser also gives back a 404.

From my first look around in `make.py`, I do not see anywhere where we are using the single parameter, except in the `init` function of `DocBuilder`. I will investigate further.
