[Proj] Add get function for searchpath (trying to protect against repeats of the proj_def.dat disaster) #300

[Roger Bivand]

Please see:

https://github.com/OSGeo/proj.4/issues/300

This relates to advice from Frank for QGIS:

http://lists.maptools.org/pipermail/proj/2013-November/006720.html

but that thread doesn't seem to lead to anything.

Roger