fix: Do not load the resilient base class for feature detection

It loaded the whole of the extensions provided by silex.sile,
which is not what we wanted outside the resilient usage.
It behaves badly with silex.sile 0.4 as overrides would now come
too late possibly, causing havoc...

packages/markdown/commands.lua

@@ -147,12 +147,32 @@ function package:loadPackageAlt(resilientpack, legacypack)
   end
 end
 
+-- For feature detection.
+-- NOTE: The previous implementation was clever;
+--   local ok, ResilientBase = pcall(require, 'classes.resilient.base')
+--   return ok and self.class:is_a(ResilientBase)
+-- However this loads the class, which loads all the silex extensions, even if
+-- the class is not used...
+-- Enforcing the silex extensions is not what we wanted.
+-- So we are back to a more naive implementation, checking the class hierarchy
+-- by name.
+-- This is lame and knows too much about internals, but heh.
+local function isResilientClass(cl)
+  while cl do
+    if cl._name == "resilient.base" then
+      return true
+    end
+    cl = cl._base
+  end
+  return false
+end
+
 function package:_init (_)
   base._init(self)
 
   -- Check if document class is a resilient class or derived from one
-  local ok, ResilientBase = pcall(require, 'classes.resilient.base')
-  self.isResilient = ok and self.class:is_a(ResilientBase)
+  self.isResilient = isResilientClass(self.class)
+  SU.debug("markdown", self.isResilient and "Used in a resilient class" or "Used in a non-resilient class")
 
   -- Only load low-level packages (= utilities)
   -- The class should be responsible for loading the appropriate higher-level