Pike 8.0: More SSL changes.

Also adds logging of SSL alerts to the debug log.
Image-Cache: Improved robustness against renderer problems.

Return error 404 to higher levels (eg the RXML parser) when
the renderer fails.

Fixes 500-errors when cimg can't find source image.
Merge branch 'patches/image-cache' into devel

* patches/image-cache:
  Image-Cache: Improved robustness against renderer problems.
Merge branch 'patches/pike8.0' into devel

* patches/pike8.0:
  Pike 8.0: More SSL changes.