Add lastError tests

Also remove a bunch of cruft in the file error-messages.m2

M2/Macaulay2/tests/normal/error-messages.m2

@@ -1,63 +1,3 @@
-stderr << "--testing the error messages must be done manually" << endl
-end
-
-X = new Type of BasicList
-x = new X from {}
-net X := x -> error "can't format this"
-
-Y = new Type of BasicList
-y = new Y from {}
-net Y := x -> while true do 1				    -- loop forever
-
-Z = new Type of X
-z = new Z from {}
-toString Z := z -> error "can't convert this to string, either!"
-
-long = w -> demark(" ",100 : w)
-p1 = long "ab" | ".  "
-p2 = long "abc" | ".  "
-p3 = long "abcd" | ".  "
-high = w -> stack(20:w)
-h1 = high "hi there"
-
-d = method(Dispatch => Thing)
-e = method(Dispatch => Thing, Options => {a=>null})
-f = method()
-g = method(Options => {a=>null})
-
-end
-
-d()
-d(3)
-d(1:3)
-d(3,4)
-d(3,4,a=>5)
-d(3,4,5,6,7,a=>5)
-e()
-e(3)
-e(1:3)
-e(3,4)
-e(3,4,a=>5)
-e(3,4,5,6,7,a=>5)
-f()
-f(3)
-f(1:3)
-f(3,4)
-f(3,4,a=>5)
-f(3,4,5,6,7,a=>5)
-g()
-g(3)
-g(1:3)
-g(3,4)
-g(3,4,a=>5)
-g(3,4,5,6,7,a=>5)
-
-d(x,y,z)
-e(x,y,z)
-f(x,y,z)
-g(x,y,z)
-
-d(x,p1,h1)
-e(x,p1,h1)
-f(x,p1,h1)
-g(x,p1,h1)
+assert((last try 1/0 else lastError()) == "division by zero")
+clearLastError()
+assert(lastError() === null)