util: convert an exception to bytes when passing to Abort()

I happened to notice this searching for how to convert an exception to bytes in
the previous patch.  I'm pretty sure I've got a bunch of other instances that
use `pycompat.bytestr()` suppressed locally.

Differential Revision: https://phab.mercurial-scm.org/D7467

mercurial/util.py

@@ -1919,7 +1919,7 b' def copyfile(src, dest, hardlink=False, '
                         ) & 0x7FFFFFFF
                         os.utime(dest, (advanced, advanced))
         except shutil.Error as inst:
-            raise error.Abort(str(inst))
+            raise error.Abort(stringutil.forcebytestr(inst))
 
 
 def copyfiles(src, dst, hardlink=None, progress=None):