Adds concat overload.

RxExample/RxExample/Examples/GitHubSignup/GitHubAPI/GitHubAPI.swift

@@ -61,8 +61,8 @@ class GitHubAPI {
     func signup(username: String, password: String) -> Observable<SignupState> {
         // this is also just a mock
         let signupResult = SignupState.SignedUp(signedUp: arc4random() % 5 == 0 ? false : true)
-        return [just(signupResult), never()]
-            .concat()
+        return just(signupResult)
+            .concat(never())
             .throttle(2, MainScheduler.sharedInstance)
             .startWith(SignupState.SigningUp)
     }

RxSwift/Observables/Observable+Multiple.swift

@@ -58,6 +58,19 @@ extension ObservableType where E : ObservableConvertibleType {
 
 // concat
 
+extension ObservableType {
+
+    /**
+    Concatenates the second observable sequence to `self` upon successful termination of `self`.
+    
+    - parameter second: Second observable sequence.
+    - returns: An observable sequence that contains the elements of `self`, followed by those of the second sequence.
+    */
+    public func concat<O: ObservableConvertibleType where O.E == E>(second: O) -> Observable<E> {
+        return [self.asObservable(), second.asObservable()].concat()
+    }
+}
+
 extension SequenceType where Generator.Element : ObservableConvertibleType {
     
     /**