Double linebreak on XMPP replaced by 1 linebreak and 1 space

[zaughon]

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I am...

• [x] Reporting a bug
• [ ] Suggesting a new feature
• [ ] Requesting help with running my bot
• [ ] Requesting help writing plugins
• [ ] Here about something else

I am running...

• Errbot version: 5.1.3
• OS version: Ubuntu 14.04 LTS
• Python version: 3.4.3
• Using a virtual environment: yes
• Backend: XMPP

Issue description

When i send a message with te\n\nst it does 1 linebreak and 1 space, instead of 2 linebreaks

E.g.:

    @botcmd()
    def test(self, msg, args):
        return "Te\n\nst"

returns:

Te
 st

instead of:

Te

st

I tried escaping it, using "```\nte\n\nst```\n", but that just returns:

\```
te
 st```

(but without the \ those were to prevent markdown from interpreting it here) Still with the 1 linebreak, and then a space.

Steps to reproduce

1. Set up a bot using XMPP-backend.
2. Create the following command:

    @botcmd()
    def test(self, msg, args):
        return "Te\n\nst"

3. Use the command.

Result: It will ignore the double line-break, and do 1 line-break, and 1 space.

Additional info

The same issue happens when using errbot templating. If you have a longer template, you can only do 1 line break, then it just start adding spaces instead, meaning everything looks extremely clumped together, as you can't really create paragraphs.

Not sure if this is related to the information/errors i posted in this comment: https://github.com/errbotio/errbot/issues/1148#issuecomment-361564907