ui: check for --debugger in sys.argv using r-string to avoid bytes on py3

Our source loader was errantly turning this --debugger into a bytes,
which was then causing me to still get a pager when I was using the
debugger on py3. That made life hard.

mercurial/ui.py

@@ -901,7 +901,7 b' class ui(object):'
             or not self.formatted()
             or self.plain()
             # TODO: expose debugger-enabled on the UI object
-            or '--debugger' in sys.argv):
+            or '--debugger' in pycompat.sysargv):
             # We only want to paginate if the ui appears to be
             # interactive, the user didn't say HGPLAIN or
             # HGPLAINEXCEPT=pager, and the user didn't specify --debug.