BadRequest message has wrong format (u"Bad Request: ...") #470

Steps to reproduce

1. Create an Updater with a valid bot token.

2. Call bot.sendMessage which will raise a BadRequest, such as with parse_mode="HTML" and text="<b>" (unclosed tag)

3. Catch the exception and read it. except BadRequest as e: look_at(e.message)

Expected behaviour

BadRequest message should say: Can't parse message text: Can't found end tag corresponding to start tag at byte offset 0

Actual behaviour

BadReqeust message actually says: u"Bad Request: Can't parse message text: Can't found end tag corresponding to start tag at byte offset 0" (notice it's literally surrounded with u" ")

Configuration

Operating System:
Debian

Version of Python, python-telegram-bot & dependencies:

$ python -m telegram
python-telegram-bot 5.2.0
urllib3 1.19.1
certifi 2016.09.26
future 0.16.0
Python 2.7.6 (default, Jun 22 2015, 17:58:13) [GCC 4.8.2]

Notes

Notice the repr(message):

https://github.com/python-telegram-bot/python-telegram-bot/blob/master/telegram/utils/request.py#L152

Should the repr call be removed, or should message have another format?