Adding FORM_PART_LIMIT for overwriting MultipartParser.part_limit

Ref: zms-publishing/ZMS#334

src/ZPublisher/HTTPRequest.py

@@ -55,6 +55,7 @@
 
 # DOS attack protection -- limiting the amount of memory for forms
 # probably should become configurable
+FORM_PART_LIMIT = 2 ** 10     # limit for individual form parts
 FORM_MEMORY_LIMIT = 2 ** 20   # memory limit for forms
 FORM_DISK_LIMIT = 2 ** 30     # disk limit for forms
 FORM_MEMFILE_LIMIT = 2 ** 12  # limit for `BytesIO` -> temporary file switch
@@ -1483,6 +1484,7 @@ def __init__(self, fp, environ):
             if content_type == "multipart/form-data":
                 parts = MultipartParser(
                     fp, options["boundary"],
+                    part_limit = FORM_PART_LIMIT,
                     mem_limit=FORM_MEMORY_LIMIT,
                     disk_limit=FORM_DISK_LIMIT,
                     memfile_limit=FORM_MEMFILE_LIMIT,