progress: split up _print() method in bar-updating and debug-printing

I just thought this was clearer, but it turned out to also simplify
the next patch.

This seems to have sped up `hg perfprogress` from 1.85 s to 1.78 s.

Differential Revision: https://phab.mercurial-scm.org/D5529

mercurial/scmutil.py

@@ -1434,7 +1434,9 b' class progress(object):'
         if total:
             self.total = total
         self.pos = pos
-        self._print(item)
+        self._updatebar(item)
+        if self.debug:
+            self._printdebug(item)
 
     def increment(self, step=1, item="", total=None):
         self.update(self.pos + step, item, total)
@@ -1443,9 +1445,9 b' class progress(object):'
         self.pos = None
         self.unit = ""
         self.total = None
-        self._print("")
+        self._updatebar("")
 
-    def _print(self, item):
+    def _updatebar(self, item):
         if getattr(self.ui._fmsgerr, 'structured', False):
             # channel for machine-readable output with metadata, just send
             # raw information
@@ -1459,9 +1461,7 b' class progress(object):'
             self.ui._progbar.progress(self.topic, self.pos, item=item,
                                       unit=self.unit, total=self.total)
 
-        if self.pos is None or not self.debug:
-            return
-
+    def _printdebug(self, item):
         if self.unit:
             unit = ' ' + self.unit
         if item: