minor: alias #read_primary? with #primary?

lib/mongo/connection.rb

@@ -470,6 +470,7 @@ def connected?
     def read_primary?
       @read_primary
     end
+    alias :primary? :read_primary?
 
     # Close the connection to the database.
     def close

lib/mongo/repl_set_connection.rb

@@ -137,6 +137,7 @@ def connecting?
     def read_primary?
       !@read_pool || @read_pool.length.zero?
     end
+    alias :primary? :read_primary?
 
     # Close the connection to the database.
     def close

test/replica_sets/connect_test.rb

@@ -32,6 +32,7 @@ def test_connect
       [RS.host, RS.ports[2]], :name => RS.name)
     assert @conn.connected?
     assert @conn.read_primary?
+    assert @conn.primary?
 
     assert_equal RS.primary, @conn.primary
     assert_equal RS.secondaries.sort, @conn.secondaries.sort

test/replica_sets/query_secondaries.rb

@@ -18,6 +18,7 @@ def teardown
 
   def test_read_primary
     assert !@conn.read_primary?
+    assert !@conn.primary?
   end
 
   def test_con