[CMake] Git Doesn't to Pull with ExternalProject_Add

[Constantine Zakkaroff]

Hello ALL,

I have a SuperBuild project (using CMake 2.8.12 on Windows Vista x64) 
depending on some other project cloned from a git repository. However 
I've noticed the cloner repository doesn't get updated when I rebuild 
the project.

Is it right to expect the repository to be updated automatically? Or 
does it need to be done manually?

Here's how the call to ExternalProject_Add looks in my project:

    ExternalProject_Add(${proj}
      GIT_REPOSITORY ${${proj}_REPOSITORY}
      GIT_TAG ${${proj}_GIT_TAG}
      SOURCE_DIR ${proj}
      BINARY_DIR ${proj}-build
      CMAKE_GENERATOR ${gen}
      CMAKE_ARGS
        -Wno-dev
        --no-warn-unused-cli
        ${COMMON_EXTERNAL_PROJECT_ARGS}
        ${${proj}_CMAKE_OPTIONS}
      INSTALL_COMMAND ""
      DEPENDS ${${proj}_DEPENDENCIES}
    )

Many thanks,
Constantine