fsharp-friendly string formatting for failed equals constraint

[et1975]

I don't know how people live with the current failed assertion messages, before:

type R = { a:int }
...
{a=1} |> should equal {a=2} // results in "expect R, but was R" kind of message!

after:

...
{a=1} |> should equal {a=2} // results in "expect {a=1}, but was {a=2}" 

Seriously, if there's a better way than this change, I'd like to know!

[sergey-tihon]

Thank you @et1975