ROS_OS_OVERRIDE is not parsed right

[davidwe]

I am getting different results in this two cases, where i think the programm should act in the same way:

case 1: "rosdep install -a --os="debian:squeeze"
case 2: "rosdep install -a" with the ROS_OS_OVERRIDE environment variable set to "debian:squeeze"

I suppose, in case 1 rosdep is working correctly, while in case 2 i get the following error for a example:
package: No definiton of [boost] for OS version[]