py3: convert diff opcode name to bytes

py3: convert diff opcode name to bytes

Differential Revision: https://phab.mercurial-scm.org/D4968

--- a/mercurial/hgweb/webutil.py	Thu Oct 11 21:22:43 2018 +0200
+++ b/mercurial/hgweb/webutil.py	Thu Oct 11 22:01:54 2018 +0200
@@ -618,6 +618,7 @@
 
 def _getcompblockgen(context, leftlines, rightlines, opcodes):
     for type, llo, lhi, rlo, rhi in opcodes:
+        type = pycompat.sysbytes(type)
         len1 = lhi - llo
         len2 = rhi - rlo
         count = min(len1, len2)