Fixing problem preventing building on VS2010 due to locate-default-setup rule being passed an undefined value.

I tested with 10.0, 11.0, 12.0, and 14.0 toolsets. The problem basically was phone-directory didn't have a value and then failure would occur calling the locate-default-setup rule. I changed to always initialize the phone-directory variable so this can't happen.

I also improved the check for below-11.0 to better match what is done for below-8.0. 

Fixes issue mentioned in the following discussion:

http://boost.2283326.n4.nabble.com/Can-t-run-tests-on-develop-tt4665008.html