Revert "fixes elm#970"

This reverts commit ae7faa7.
This patch was not correct and was causing a compiler error due to not explicitly import == and /= in Char.elm

src/Char.elm

@@ -66,42 +66,46 @@ type Char = Char -- NOTE: The compiler provides the real implementation.
 -- CLASSIFICATION
 
 
-{-| Detect upper case Unicode characters.
+{-| Detect upper case ASCII characters.
 
     isUpper 'A' == True
     isUpper 'B' == True
     ...
     isUpper 'Z' == True
-    
-    isUpper 'Σ' == True
 
     isUpper '0' == False
     isUpper 'a' == False
     isUpper '-' == False
+    isUpper 'Σ' == False
 -}
 isUpper : Char -> Bool
 isUpper char =
-  (char == Char.toUpper char)
-    && (char /= Char.toLower char)
+  let
+    code =
+      toCode char
+  in
+    code <= 0x5A && 0x41 <= code
 
 
-{-| Detect lower case Unicode characters.
+{-| Detect lower case ASCII characters.
 
     isLower 'a' == True
     isLower 'b' == True
     ...
     isLower 'z' == True
-    
-    isLower 'π' == True
 
     isLower '0' == False
     isLower 'A' == False
     isLower '-' == False
+    isLower 'π' == False
 -}
 isLower : Char -> Bool
 isLower char =
-  (char == Char.toLower char)
-    && (char /= Char.toUpper char)
+  let
+    code =
+      toCode char
+  in
+    0x61 <= code && code <= 0x7A
 
 
 {-| Detect upper case and lower case ASCII characters.