deprecation: gate deprecation warning behind devel configuration

Regular users are not supposed to be exposed to the API deprecation warnings.
We now only issue them when the developper warnings are enabled.

mercurial/ui.py

@@ -1161,6 +1161,9 b' class ui(object):'
         - msg: message explaining what is deprecated and how to upgrade,
         - version: last version where the API will be supported,
         """
+        if not (self.configbool('devel', 'all-warnings')
+                or self.configbool('devel', 'deprec-warn')):
+            return
         msg += ("\n(compatibility will be dropped after Mercurial-%s,"
                 " update your code.)") % version
         self.develwarn(msg, stacklevel=2)