convert/svn: handle MissingTool exception from converter_sink class

The converter_sink class had no way of handling MissingTool
exception. This change makes it to abort when there is a
MissingTool exception.

hgext/convert/convcmd.py

@@ -70,6 +70,8 b' def convertsink(ui, path, type):'
                 return sink(ui, path)
         except NoRepo, inst:
             ui.note(_("convert: %s\n") % inst)
+        except MissingTool, inst:
+            raise util.Abort(_('%s\n') % inst)
     raise util.Abort(_('%s: unknown repository type') % path)
 
 class progresssource(object):