Refactor rosbash.fish w/ fish compatible syntax

When ROS added support to fish, the recommended procedure was using
source.bash and then manually source rosfish. In this flow,
rosbash.fish env hook was never called. To add native support to fish
(see ros/catkin#1168), it is needed to ensure
consistency along files (scripts ended w/ .fish should be compatible w/
fish)

tools/rosbash/env-hooks/15.rosbash.fish.em

@@ -1,10 +1,10 @@
 # generated from rosbash/env-hooks/15.rosbash.fish.em
 
 @[if DEVELSPACE]@
-. "@(CMAKE_CURRENT_SOURCE_DIR)/rosfish"
+source "@(CMAKE_CURRENT_SOURCE_DIR)/rosfish"
 @[else]@
-if [ -z "$CATKIN_ENV_HOOK_WORKSPACE" ]; then
-  CATKIN_ENV_HOOK_WORKSPACE="@(CMAKE_INSTALL_PREFIX)"
-fi
-. "$CATKIN_ENV_HOOK_WORKSPACE/share/rosbash/rosfish"
+if test -z "$CATKIN_ENV_HOOK_WORKSPACE"
+    set CATKIN_ENV_HOOK_WORKSPACE "@(CMAKE_INSTALL_PREFIX)"
+end
+source "$CATKIN_ENV_HOOK_WORKSPACE/share/rosbash/rosfish"
 @[end if]@