Better extension conflict resolution from upstream

Author: zayass

Foundation/NSError.swift

@@ -296,23 +296,13 @@ extension CustomNSError where Self: RawRepresentable, Self.RawValue: SignedInteg
     public var errorCode: Int {
         return numericCast(self.rawValue)
     }
-    
-    // conflict resolution
-    public var _code: Int {
-        return errorCode
-    }
 }
 
 extension CustomNSError where Self: RawRepresentable, Self.RawValue: UnsignedInteger {
     // The error code of Error with integral raw values is the raw value.
     public var errorCode: Int {
         return numericCast(self.rawValue)
     }
-    
-    // conflict resolution
-    public var _code: Int {
-        return errorCode
-    }
 }
 
 public extension Error where Self : CustomNSError {
@@ -323,6 +313,16 @@ public extension Error where Self : CustomNSError {
     var _code: Int { return self.errorCode }
 }
 
+public extension Error where Self: CustomNSError, Self: RawRepresentable, Self.RawValue: SignedInteger {
+    /// Default implementation for customized NSErrors.
+    var _code: Int { return self.errorCode }  
+}
+
+public extension Error where Self: CustomNSError, Self: RawRepresentable, Self.RawValue: UnsignedInteger {
+    /// Default implementation for customized NSErrors.
+    var _code: Int { return self.errorCode }  
+}
+
 public extension Error {
     /// Retrieve the localized description for this error.
     var localizedDescription: String {