Backed out changeset: 572f81d256a2
Enhance debugging views

* SymbolicExpression: shows its internal object type.
* Vector: shows its length and elements.
* Matrix: shows its size and elements.
* DataFrame: shows its size and columns' info.
* InternalString: shows its internal string representation.
Add Factor class.
Replace constant.
Creates a new solution file

* R.NET.sln contains only production projects.
* R.NET.Tests.sln contains all (identical to the old R.NET.sln).
Add GetSlice overloading methods for F#

* Matrix.GetSlice -> Vector will be supported in F# 3.1,
  and tests cannot be compiled without the version.
Add nuspec.