This commit fixes a situation in which, when an error happens while
decoding the content of a multiset, a temporary array would leak.

Thanks to Joshua Rogers <jrogers@opera.com> for the report.

This commit fixes a use-after-free when a delay encoded tag overrides
the container being decoded right now.

Thanks to Joshua Rogers <jrogers@opera.com> for the report.

* tobij/fix-image-xwd-decoding:
  Image.XWD: Further improve size check

Thanks to Cezary Cerekwicki <ccerekwicki@opera.com> for the report.

Fixes warnings on versions of Linux where mallinfo(3C) has
been deprecated.

* tobi/fix-image-x-decoding:
  Image.X: Fix calls of alloca().