Reversing the list of assemblies loaded in the domain before unloading.

Changes made in df4a73d70f6b7c388a23d4d2984337b97ce640db and a736dee9e1511a0d3ff87ff14fe46459c03dd73b reversed the order in which assemblies were added to the domain_assemblies list by appending instead of prepending. This results in the assemblies being unloaded in the reverse order from prior to these changes and can result in a crash unloading assemblies that have generics referenced in a dynamic assembly that was created after the assembly containing the generic type.