Merge pull request #5157 from lambdageek/bug-57850+57851-2017-06
[sre] Deal with ResolveEventHandler returning an AssemblyBuilder (Fixes #57850, #57851)
Fix a couple of bugs in the situation where a ResolveEventHandler happens to return an AssemblyBuilder.
#57850 - if the ResolveEventHandler returns a reflection only assembly, throw a FileNotFoundException
#57851 - don't look for a ReferenceAssemblyAttribute on assemblies returned by a ResolveEventHandler if they happen to be an AssemblyBuilder. (the native code path to get there is to try and instantiate a custom attribute in some other assembly, hence the fairly convoluted test in assemblyresolve_event5 and its helper files)