internals: copy-edit "register" -> "registrar" in configitem docs

mercurial/help.py

@@ -202,7 +202,7 b' internalstable = sorted(['
      loaddoc('censor', subdir='internals')),
     (['changegroups'], _('Changegroups'),
      loaddoc('changegroups', subdir='internals')),
-    (['config'], _('Config Register'),
+    (['config'], _('Config Registrar'),
      loaddoc('config', subdir='internals')),
     (['requirements'], _('Repository Requirements'),
      loaddoc('requirements', subdir='internals')),

mercurial/help/internals/config.txt

@@ -88,7 +88,7 b' The ``dynamicdefault`` object is then av'
 Supporting older versions
 -------------------------
 
-The registry was introduced in Mercurial 4.3, and the ``generic`` parameter was
+The registrar was introduced in Mercurial 4.3, and the ``generic`` parameter was
 introduced in 4.4. Starting with Mercurial 4.4, all core options were registered
 and developer warnings are emitted when accessing unregistered option.