Improve wording of "cannot find" errors

pelican/contents.py

@@ -310,6 +310,6 @@ def is_valid_content(content, f):
         content.check_properties()
         return True
     except NameError as e:
-        logger.error("Skipping %s: impossible to find information about "
+        logger.error("Skipping %s: could not find information about "
                       "'%s'" % (f, e))
         return False

pelican/settings.py

@@ -160,7 +160,7 @@ def configure_settings(settings):
         if os.path.exists(theme_path):
             settings['THEME'] = theme_path
         else:
-            raise Exception("Impossible to find the theme %s"
+            raise Exception("Could not find the theme %s"
                             % settings['THEME'])
 
     # if locales is not a list, make it one