When using WinMD projects in the IDE it is easy to run into
a situation where a project references a project and an assembly
and the project also references the assembly.

For example, a C# compilation C1 references a C# WinMD project C2
and a .winmd assembly W1. W1 also references C2.

When binding these references for C1 we hit a problem -- because
the ContentType of a compilation in Roslyn is always Default (the
compiler emits .winmdobjs, which are later turned into .winmds by
winmdexp, the metadata reference from W1 to C2 will never unify
(different ContentTypes). This change modifies the reference manager to
do a special check for this case and see if we are using a winmdobj
compilation and, if so, correctly unify the reference and the
definition.