SERVER-12128 Inconsistent earth radius used in tests

Resolves #580

jstests/core/geo_array2.js

@@ -78,8 +78,8 @@ for( var i = -1; i < 2; i++ ){
 				
 		// Do nearSphere check
 		
-		// Earth Radius
-		var eRad = 6371
+		// Earth Radius from geoconstants.h
+		var eRad = 6378.1
 				
 		nearResults = db.geoarray2.find( { loc : { $nearSphere : center , $maxDistance : 500 /* km */ / eRad }, type : type } ).toArray()
 		

jstests/core/geo_center_sphere2.js

@@ -28,7 +28,7 @@ for ( var test = 0; test < numTests; test++ ) {
     Random.srand( 1337 + test );
 
     var radius = 5000 * Random.rand(); // km
-    radius = radius / 6371; // radians;
+    radius = radius / 6378.1; // radians; earth radius from geoconstants.h
     var numDocs = Math.floor( 400 * Random.rand() );
     // TODO: Wrapping uses the error value to figure out what would overlap...
     var bits = Math.floor( 5 + Random.rand() * 28 );

src/mongo/db/geo/geoconstants.h

@@ -30,7 +30,8 @@
 
 namespace mongo {
 
-    // Thanks, Wikipedia.
+    // Equatorial radius of earth.
+    // Source: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html
     const double kRadiusOfEarthInMeters = (6378.1 * 1000);
 
 }  // namespace mongo