Incorrect expect error "not" messages

[luttje]

Most expects do not check for self.inverse to see if the error should say it did 'not' match expected value. This causes confusing errors when using the ["not"] modifier.

Atm each matcher needs to manually check and format the error with something like .. (expect.inverse and " not" or "") ..

It would be nicer if (like expect:checkEquals) there is a expect:throwUnexpected. Or that the checkEquals would work more like a guardEquals like this:

local function toBe(expect, expected)
  local actual = expect.actual

  -- Old:
  -- if not expect:checkEquals(actual, expected) then
  --   error("Expected " .. tostring(actual) .. (expect.inverse and " not " or "") .. " to be " .. tostring(expected))
  -- end

  -- New concept:
  expect:guardEquality(actual, expected, "to be")

  return true
end