Work around trytond.module not being a real namespace module.

Solution is to add all trytond module's locations to
trytond.modules._path__. This will make trytond.module behave much
like a namespace module.
Adding to __path__ is done in update_egg_modules() to ensure __path__
is updated whenever the list of egg modules is updated.

*** a/trytond/modules/__init__.py	1970-01-01 01:00:01.000000000 +0100
--- b/trytond/modules/__init__.py	2021-12-02 18:12:15.385101986 +0100
***************
*** 38,43 ****
--- 38,46 ----
          import pkg_resources
          for ep in pkg_resources.iter_entry_points('trytond.modules'):
              EGG_MODULES[ep.name] = ep
+             path = os.path.join(ep.dist.location, 'trytond', 'modules')
+             if not path in __path__ and os.path.isdir(path):
+                 __path__.append(path)
      except ImportError:
          pass
  
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<tr class='logheader'><td><span title='2021-11-19 23:04:19 +0100'>2021-11-19</span></td><td class='logsubject'><a href='/guix/commit/nix/libutil?id=24224530d1f4a70808d003ba8dce849b77625b79'>daemon: Micro-optimize 'deletePath'.</a></td><td>Ludovic Courtès</td></tr>
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'remove' calls 'unlink' first and falls back to 'rmdir' upon EISDIR.
This change gets rid of the 'unlink' call for every directory being
removed.

* nix/libutil/util.cc (_deletePath): Call 'unlink' or 'rmdir' depending
on 'st.st_mode', rather than call 'remove'.


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