scriptapi: Sort out ServerEnvironment / Environment distinction properly

The API implementation is shared between CSM and SSM.
Functions should retrieve a plain env when they do not
need any server-specific functions.

src/environment.cpp

@@ -83,6 +83,24 @@ float Environment::getTimeOfDayF()
 	return m_time_of_day_f;
 }
 
+bool Environment::line_of_sight(v3f pos1, v3f pos2, v3s16 *p)
+{
+	// Iterate trough nodes on the line
+	voxalgo::VoxelLineIterator iterator(pos1 / BS, (pos2 - pos1) / BS);
+	do {
+		MapNode n = getMap().getNode(iterator.m_current_node_pos);
+
+		// Return non-air
+		if (n.param0 != CONTENT_AIR) {
+			if (p)
+				*p = iterator.m_current_node_pos;
+			return false;
+		}
+		iterator.next();
+	} while (iterator.m_current_index <= iterator.m_last_index);
+	return true;
+}
+
 /*
 	Check if a node is pointable
 */