Add support for LPOP and BRPOP

[anujphadke]

Usage -

1. blpop key [key...] timeout
2. brpop key [key...] timeout

E.g. -

1. blpop:
   127.0.1.1:8102> LPUSH test_list how
   (integer) 1
   127.0.1.1:8102> LPUSH test_list are
   (integer) 2
   127.0.1.1:8102> LPUSH test_list you
   (integer) 3
   127.0.1.1:8102> blpop test_list 1

1. "test_list"
2. "you"
   127.0.1.1:8102> blpop test_list 1
3. "test_list"
4. "are"
   127.0.1.1:8102> blpop test_list 1
5. "test_list"
6. "how"
   127.0.1.1:8102> blpop test_list 1

2. brpop :
   127.0.1.1:8102> LPUSH test_list how
   (integer) 1
   127.0.1.1:8102> LPUSH test_list are
   (integer) 2
   127.0.1.1:8102> LPUSH test_list you
   (integer) 3
   127.0.1.1:8102> brpop test_list 1

1. "test_list"
2. "how"
   127.0.1.1:8102> brpop test_list 1
3. "test_list"
4. "are"
   127.0.1.1:8102> brpop test_list 1
5. "test_list"
6. "you"

[w4096]

blpop may block the connection between proxy and Redis, and the connection was reused by many client. This implementation can not work.