Make K_TIMEOUT configurable and rename

Let's make K_TIMEOUT configurable via an environment variable, so that this stays generically useful but django can still set it.

``` python
TIMEOUT = os.env.get('SPHINX_TIMEOUT', 1)
```

Then Django can put, in `settings`:

``` python
os.env['SPHINX_TIMEOUT', 5)
```

That should work, if I understand the order of the imports. Will double test and implement.
