Currently fatal errors look like this:

<div class="box errorbox"><p class="errormessage">A required parameter (id) was missing</p><p class="errorcode"><a href="http://docs.moodle.org/26/en/error/moodle/missingparam">More information about this error</a></p></div>

we should add bootstrap classes so they render like Bootstrap Danger/Error Alerts:

<div class="box errorbox alert alert-error"><p class="errormessage">A required parameter (id) was missing</p><p class="errorcode"><a href="http://docs.moodle.org/26/en/error/moodle/missingparam">More information about this error</a></p></div>

or for Bootstrap v3 (error -> danger, add alert class on link)

<div class="box errorbox alert alert-danger"><p class="errormessage">A required parameter (id) was missing</p><p class="errorcode"><a class="alert-link" href="http://docs.moodle.org/24/en/error/moodle/missingparam">More information about this error</a></p></div>

This all currently happens here:

https://github.com/moodle/moodle/blob/master/lib/outputrenderers.php#L2577-L2584

In order to make it easier to make this change, and allow for future upgrades, the bit that outputs the error should be extracted into it's own renderer first