Fix off by 2 error in EXEC reply handling

The EXEC reply should have the same number of replies as there are commands in
the MULTI. This line of code expected the MULTI and EXEC commands themselves to
be part of the futures array, but they are not.

Note that this only surfaces for Redis versions < 2.6.5, because that is when
the EXECABORT error reply was introduced. Also see: antirez/redis@41f0f92.

Author: pietern

lib/redis/pipeline.rb

@@ -78,7 +78,7 @@ def finish(replies)
         # EXEC command failed.
         raise exec if exec.is_a?(CommandError)
 
-        if exec.size < futures.size - 2
+        if exec.size < futures.size
           # Some command wasn't recognized by Redis.
           raise replies.detect { |r| r.is_a?(CommandError) }
         end

test/pipelining_commands_test.rb

@@ -93,9 +93,7 @@ def test_assignment_of_results_inside_the_block_with_errors
       r.pipelined do
         r.doesnt_exist
         @first = r.sadd("foo", 1)
-        r.doesnt_exist
         @second = r.sadd("foo", 1)
-        r.doesnt_exist
       end
     end
 

test/transactions_test.rb

@@ -67,9 +67,7 @@ def test_assignment_inside_multi_exec_block_with_immediate_command_errors
       r.multi do |m|
         m.doesnt_exist
         @first = m.sadd("foo", 1)
-        m.doesnt_exist
         @second = m.sadd("foo", 1)
-        m.doesnt_exist
       end
     end