Use string to describe namelist option for building_temp_method to make user-interface more clear

**Erik Kluzek < erik > - 2014-10-20 09:02:44 -0600**
**Bugzilla Id:** [2068](http://bugz.cgd.ucar.edu/show_bug.cgi?id=2068)
**Bugzilla CC:** oleson,

Instead of using an integer in the namelist for urban building temperature method, use a string to make it more clear in the namelist, and then then an integer in the code (faster and ensures correct values on compilation).