setdiscovery: factorize similar sampling code

We are using full sampling of 'fullsamplesize' in both case. The only
difference is the debug message. So we factorise the sampling code and put the
message in an extra conditional.

This is going to help making changes around the sampling logic. Such changes are
needed to improve discovery performance on highly headed repository.

mercurial/setdiscovery.py

@@ -197,13 +197,11 b' def findcommonheads(ui, local, remote,'
         if not undecided:
             break
 
-        if full:
-            ui.note(_("sampling from both directions\n"))
-            sample = _takefullsample(dag, undecided, size=fullsamplesize)
-            targetsize = fullsamplesize
-        elif common.hasbases():
-            # use cheapish initial sample
-            ui.debug("taking initial sample\n")
+        if full or common.hasbases():
+            if full:
+                ui.note(_("sampling from both directions\n"))
+            else:
+                ui.debug("taking initial sample\n")
             sample = _takefullsample(dag, undecided, size=fullsamplesize)
             targetsize = fullsamplesize
         else: