make external_auth table searchable in django admin; fix

missed instance of login link which should have been behind DISABLE_LOGIN_BUTTON

common/djangoapps/external_auth/admin.py

@@ -5,4 +5,8 @@ django admin pages for courseware model
 from external_auth.models import *
 from django.contrib import admin
 
-admin.site.register(ExternalAuthMap)
+class ExternalAuthMapAdmin(admin.ModelAdmin):
+    search_fields = ['external_id','user__username']
+    date_hierarchy = 'dtcreated'
+
+admin.site.register(ExternalAuthMap, ExternalAuthMapAdmin)

lms/templates/portal/course_about.html

@@ -76,7 +76,11 @@
 	             <div id="register_message"></div>
             %endif
         %else:
-            <a href="#signup-modal" class="register" rel="leanModal" data-notice='You must Sign Up or <a href="#login-modal" rel="leanModal">Log In</a> to enroll.'>Register for ${course.number}</a>
+            <a href="#signup-modal" class="register" rel="leanModal" data-notice='You must Sign Up
+% if not settings.MITX_FEATURES['DISABLE_LOGIN_BUTTON']:
+		     or <a href="#login-modal" rel="leanModal">Log In</a>
+% endif
+		     to enroll.'>Register for ${course.number}</a>
         %endif
         </div>