Add an option to set timeout for mget requests

Hello @x-ma, 

Please review the following commits I made in branch 'satya-timeout-per-request'.

510616f9789fddcaf9e5d77ebfa849055a734918 (2014-09-10 11:03:21 -0700)
Add an option to set timeout for mget requests

R=@x-ma
You don't need to modify this private variable directly.