Fixed broken Mumble log links on large text messages

Fix of issue #1188.  If a text message was too big to be displayed in the log, it would be converted to plain text, including any Mumble prefix containing user or channel links.  This PR prevents those links from being converted to plain text, as seen below:

**Before patch**:
![Before](https://cloud.githubusercontent.com/assets/110883/2687257/821936a0-c245-11e3-815e-4b71c684c43f.png)

**With patch**:
![With](https://cloud.githubusercontent.com/assets/110883/2687258/821a83a2-c245-11e3-848f-8a65c0bd7e43.png)