=========================
* Further adapting to naming changes in raster ("x" argument)
* Making the same change in gdistance ("x" is the first argument in any function)
* Bug fix in resistanceDistance: uncomment reproject
* Improved documentation of definitions of different distance functions
* Dependency on igraph0 -- to be changed to igraph 0.6 after May 31, 2012
* Removed initialize functions, using prototypes instead