new getProjection() method for map or layer classes

[bruno_gendron@…]

Request to add a new method to map and layer classes: getProjection().

The method should return a string, or even better, an array of strings with 
proj4 parameters (if any) of map or layer.

Could be VERY useful in cases when you want to get user-input in some 
coordinate system and convert this input to map coordinates without previously 
knowing the projection of the map.

[assefa]

Added