imagemagick: upgrade to 6.7.5 because 6.4.4 is not compatible with zlib-1.2.6 we have now

* for zlib-1.2.6 issue see:
  http://www.imagemagick.org/discourse-server/viewtopic.php?f=2&t=20267
* dist-lzip removed because it's not supported in our automake yet
* xml is explicity disabled, wasn't enabled before and if autodetected
  then fails (see comment above EXTRA_OECONF).
* LIC_FILES_CHKSUM updated, only formal changes AFAIK see:
  http://trac.imagemagick.org/log/ImageMagick/trunk/LICENSE


  for details
* empty dirs coders and filters added to PN to fix QA warning

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>