Fix path mangling in reftest list

The reftest list for gradients had somehow got damaged, and paths missed
a few characters. Fixed that.
Fix a few mistakes in reftest.list files
Convert old fashioned reftest lists into link tags

Replaces reftest.list files with the equivalent link tag in relevant
files, as reftest.list is considered deprecated.

Conversion done using: https://github.com/frivoal/reftest-converter
Merge pull request #14 from frivoal/reftests

Reftest updates from frivoal