ui: convert stack traces to sysbytes before logging They're coming back as unicodes, so sysbytes seems like the best we can do. This is like D2171 and D2172, but those fail on Python 2.7.5 (seriously!), so this is my version of the same change. I actually wrote this before reviewing those, then discarded it, then came back to it after finding out 2.7.5 is a silly place. Differential Revision: https://phab.mercurial-scm.org/D2209