patches: fixed linking to SDL library in map_server

[meyerj]

Fixes linking to libSDLmain.a and libSDL.a in downstream packages.

find_package(SDL REQUIRED)

(with FindSDL.cmake provided by cmake) only sets SDL_LIBRARY and SDL_INCLUDE_DIR (without the trailing S). But catkin_package(DEPENDS <prefix>) looks for <prefix>_INCLUDE_DIRS and <prefix>_LIBRARIES. catkin emits a warning if neither of both is set for a dependency listed in DEPENDS, which should actually be treated as an error. Or catkin could accept multiple commonly used suffixes for include directories and libraries because apparently there is no standard. See related issue ros/catkin#552.

In any case listing SDL in catkin_package(DEPS ...) is equivalent to listing include directories and libraries in INCLUDE_DIRS and LIBRARIES argument lists.

Another candidate to submit a patch upstream (#81).

[jubeira]

Tested patch, LGTM!