Update csharp test to identify .net fwk version

[darrelmiller]

The version property previously used to identify the useragent only identified the CLR, not the framework version. I suspect the previous tests were run on .net 4.0. Running the tests on .Net 4.5 show a reasonable number of differences, including differences in how the [] are handled and how ipv6 addresses are rendered.

[rubys]

When I try compiling with this, I get

testuri.cs(67,60): error CS0246: The type or namespace name
        'TargetFrameworkAttribute' could not be found (are you missing a using
        directive or an assembly reference?)
testuri.cs(67,92): error CS0246: The type or namespace name
        'TargetFrameworkAttribute' could not be found (are you missing a using
        directive or an assembly reference?)

[rubys]

Looks like this may be new with .Net Framework 4.5. I'll try to update and see what happens.