API: changed default behavior concerning earth radius.
API: changed default behavior concerning earth radius.

now chooses local approximation to earh radius introduced by Edouard if re is
not given explicitly.

--HG--
branch : feature/georef

wradlib/wradlib,heistermann/wradlib,heistermann/wradlib,wradlib/wradlib,kmuehlbauer/wradlib,kmuehlbauer/wradlib