Fixes KVO observer leak in FBLoginView

Summary:
FBLoginView was registering for KVO observation twice on any active
session that became active at the time that the FBLoginView first fetched
the session. The fix moves the current active-session wire-up before
the global observation for active session.

Test Plan: Ran tests, ran hello facebook sample

Reviewers: clang, gregschechte

Reviewed By: clang

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D540267

Task ID: 1235919

scripts/build_distribution.sh

@@ -69,6 +69,8 @@ mkdir -p $FB_SDK_BUILD_PACKAGE_DOCS
   || die "Could not copy $$FB_SDK_FRAMEWORK_DOCS/docset/Contents"
 \cp $FB_SDK_ROOT/README $FB_SDK_BUILD_PACKAGE/Documents/FacebookSDK \
   || die "Could not copy README"
+\cp $FB_SDK_ROOT/LICENSE $FB_SDK_BUILD_PACKAGE/Documents/FacebookSDK \
+  || die "Could not copy LICENSE"
 
 # -----------------------------------------------------------------------------
 # Fixup projects to point to the SDK framework

src/FBLoginView.m

@@ -133,6 +133,9 @@ - (void)initialize {
     [FBSession openActiveSessionWithPermissions:self.permissions
                                    allowLoginUI:NO
                               completionHandler:nil];
+
+    // wire-up the current session to the login view, before adding global session-change handlers
+    [self wireViewForSession:FBSession.activeSession];
 
     [[NSNotificationCenter defaultCenter] addObserver:self 
                                              selector:@selector(handleActiveSessionSetNotifications:) 
@@ -144,8 +147,6 @@ - (void)initialize {
                                                  name:FBSessionDidUnsetActiveSessionNotification
                                                object:nil]; 
 
-    [self wireViewForSession:FBSession.activeSession];
-
     // setup button
     self.button = [UIButton buttonWithType:UIButtonTypeCustom];
     [self.button addTarget:self