The default patch file viewer is messy (ie. no side by side diff view etc). I tried setting the path of beyondCompare exe in \"Settings->Unified Diff Viewer->custom\", but beyon
You can view a diff file (a patch generated by diff tool) using Kompare from KDE environment. I used it before on Linux, but today I found how to install it on Windows. Here is an installation instruction from a blog "Kompare - the only valuable diff for M$Windows":
You can also add an association with .diff file format and now you can view any diff files. For me it works great.