util: convert traceback-related sysstrs to sysbytes in getstackframes

With this change, test-devel-warnings.t passes except for differences
in how ProgrammingError is formatted and one mysterious traceback
inside of transaction.__del__.

Differential Revision: https://phab.mercurial-scm.org/D2212

mercurial/util.py

@@ -3171,7 +3171,7 b" def getstackframes(skip=0, line=' %-*s i"
 
     Not be used in production code but very convenient while developing.
     '''
-    entries = [(fileline % (fn, ln), func)
+    entries = [(fileline % (pycompat.sysbytes(fn), ln), pycompat.sysbytes(func))
         for fn, ln, func, _text in traceback.extract_stack()[:-skip - 1]
         ][-depth:]
     if entries: