- Drop patches not meintioned in the changelog ever:
* GraphicsMagick-debian-fixed.patch
* GraphicsMagick-include.patch
* GraphicsMagick-perl-link.patch
* The package builds just fine without them and there is no
refference explaining it
- Convert the deps to pkgconfig variants where possible.

- Version update to 1.3.26:
* DPX: Fix excessive use of memory (DOS issue) due to file header
claiming large image dimensions but insufficient backing
data. (CVE-2017-10799 bsc#1047054).
* JNG: Fix memory leak when reading invalid JNG image (CVE-2017-8350).
* MAT: Fix excessive use of memory (DOS issue) due to continuing
processing with insufficient data and claimed large image
size. Verify each file extent to make sure that it is within range
of file size. (CVE-2017-10800 bsc#1047044).
* META: Fix heap overflow while parsing 8BIM chunk (CVE-2016-7800).
* PCX: Fix denial of service issue.
* RLE: Fix abnomally slow operation (denial of service issue) with
intentionally corrupt colormapped file.
* PICT: Fix possible buffer overflow vulnerability given suitably
truncated input file.
* PNG: Enforce spec requirement that the dimensions of the JPEG
embedded in a JDAT chunk must match the JHDR dimensions
(CVE-2016-9830).
* PNG: Avoid NULL dereference when MAGN chunk processing fails.
* SCT: Fix stack-buffer read overflow (underflow?) while reading SCT
header.
* SGI: Fix denial of service issues. Delay large memory allocations (forwarded request 511776 from scarabeus_iv)