installing STIR with local extension libraries

[danieldeidda]

when installing STIR with local libraries the extra_dir.cmake file needs to set STIR_LIBRARIES and STIR_REGISTRIES parent variable as follows:

`

add include directory to compiler switches

include_directories(${STIR_LOCAL}/include)
include_directories(${CMAKE_SOURCE_DIR}/src/local/include)

add registries

list(APPEND STIR_REGISTRIES
${STIR_LOCAL}/your_local/local_registries.cxx)

list(APPEND STIR_LIBRARIES local_buildblock)

copy to PARENT_SCOPE

SET( STIR_REGISTRIES ${STIR_REGISTRIES} PARENT_SCOPE)
SET( STIR_LIBRARIES ${STIR_LIBRARIES} PARENT_SCOPE)

add_subdirectory( ${STIR_LOCAL}/your_buildblock local/your_buildblock)
add_subdirectory( ${STIR_LOCAL}/your_utilities local/your_utilities)
`