Fixed image captions by resetting caption_lines for each new image. Before, the…

Fixed image captions by resetting caption_lines for each new image.  Before, the n-th image would have the first n captions concatenated together.

wiki/plugins/images/markdown_extensions.py

@@ -40,6 +40,7 @@ class ImagePreprocessor(markdown.preprocessors.Preprocessor):
                 except models.Image.DoesNotExist:
                     pass
                 line = line.replace(m.group(1), "")
+                caption_lines = []
             elif previous_line_was_image:
                 if line.startswith("    "):
                     caption_lines.append(line[4:])