Merge: Useless type

Fix a wrong `useless-type` warning for attributes.
Extends the `useless-type` warning to local variables.

Pull-Request: #945

diff --combined lib/standard/string.nit
index 62d5ddc,558d9eb..e17d2cf
--- 1/lib/standard/string.nit
--- 2/lib/standard/string.nit
+++ b/lib/standard/string.nit
@@@ -1405,7 -1405,7 +1405,7 @@@ abstract class Buffe
        #
        # SEE: `Char::is_letter` for the definition of a letter.
        #
 -      #    var b = new FlatBuffer.from("jAVAsCriPt")"
 +      #    var b = new FlatBuffer.from("jAVAsCriPt")
        #    b.capitalize
        #    assert b == "Javascript"
        #    b = new FlatBuffer.from("i am root")
@@@ -1418,7 -1418,7 +1418,7 @@@
                if length == 0 then return
                var c = self[0].to_upper
                self[0] = c
-               var prev: Char = c
+               var prev = c
                for i in [1 .. length[ do
                        prev = c
                        c = self[i]