ZODB Components: Display proper traceback and source code if an error occurred on 'exec'.

The initial 'exec' traceback was not passed when raising ImportError (following
PEP-302), thus it displayed traceback in component_package instead of the actual
location of the error. Also, Caching source code retrieved from traceback/(i)pdb
(through get_source()) was done after the actual 'exec', whereas it should have
always been *before* obviously...

Steps to reproduce:
  1/ Create and validate a Test Component A importing another Component B.
  2/ Invalidate Component B or add a typo not handled by pylint (because of exceptions).

product/ERP5Type/dynamic/component_package.py

@@ -347,6 +347,13 @@ class ComponentDynamicPackage(ModuleType):
       # This must be set for imports at least (see PEP 302)
       module.__file__ = '<' + relative_url + '>'
 
+      # Only useful for get_source(), do it before exec'ing the source code
+      # so that the source code is properly display in case of error
+      module.__loader__ = self
+      module.__path__ = []
+      module.__name__ = module_fullname
+      self.__fullname_source_code_dict[module_fullname] = source_code_str
+
       try:
         # XXX: Any loading from ZODB while exec'ing the source code will result
         # in a deadlock
@@ -357,13 +364,9 @@ class ComponentDynamicPackage(ModuleType):
         if module_fullname_alias:
           del sys.modules[module_fullname_alias]
 
-        raise ImportError("%s: cannot load Component %s (%s)" % (fullname,
-                                                                 name,
-                                                                 error))
-
-      module.__path__ = []
-      module.__loader__ = self
-      module.__name__ = module_fullname
+        raise ImportError(
+          "%s: cannot load Component %s (%s)" % (fullname, name, error)), \
+          None, sys.exc_info()[2]
 
       # Add the newly created module to the Version package and add it as an
       # alias to the top-level package as well
@@ -388,9 +391,6 @@ class ComponentDynamicPackage(ModuleType):
 
       module_cache_set.add(module)
 
-      # Only useful for get_source()
-      self.__fullname_source_code_dict[module_fullname] = source_code_str
-
       return module
     finally:
       # load_module() can be called outside of import machinery, for example