Unit test stack traces missing file and line info

On some mono environments when unit tests fail we get a stack trace that
is missing the file and line details making debugging more difficult.

This is due to us running a pre-compiled NUnit assembly that references
version 2.0.0.0 of mscorlib which can be seen here:

	$ monodis Tools/NUnit-2.6.1/bin/nunit-console.exe
	.assembly extern mscorlib
	{
	  .ver 2:0:0:0
	  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) // .z\V.4..
	}

	...

This commit adds command line options to mono when running the test target
to a) force debugging info and b) force the use of the v4.0 profile.