Update ExternalProject definition to explicitly specify GIT_TAG

Branch name are also prefixed using "origin/", doing so will ensure
that the changes fetched bu ExternalProject cmale module are checked out.

CMakeExternals/CTKData.cmake

@@ -18,6 +18,7 @@ IF(BUILD_TESTING)
   #   MESSAGE(STATUS "Adding project:${proj}")
     ExternalProject_Add(${proj}
       GIT_REPOSITORY ${git_protocol}://github.com/commontk/CTKData.git
+      GIT_TAG "origin/master"
       CONFIGURE_COMMAND ""
       BUILD_COMMAND ""
       INSTALL_COMMAND ""

CMakeExternals/DCMTK.cmake

@@ -23,7 +23,7 @@ IF(${add_project})
 
     ExternalProject_Add(${proj}
         GIT_REPOSITORY "${git_protocol}://github.com/commontk/DCMTK.git"
-        GIT_TAG "patched"
+        GIT_TAG "origin/patched"
         CMAKE_GENERATOR ${gen}
         BUILD_COMMAND ""
         CMAKE_ARGS

CMakeExternals/Log4Qt.cmake

@@ -21,7 +21,7 @@ IF(${add_project})
 #     MESSAGE(STATUS "Adding project:${proj}")
     ExternalProject_Add(${proj}
       GIT_REPOSITORY "${git_protocol}://github.com/commontk/Log4Qt.git"
-      GIT_TAG "patched"
+      GIT_TAG "origin/patched"
       CMAKE_GENERATOR ${gen}
       BUILD_COMMAND ""
       CMAKE_ARGS

CMakeExternals/PythonQt.cmake

@@ -35,7 +35,7 @@ IF(${add_project})
       
     ExternalProject_Add(${proj}
       GIT_REPOSITORY "${git_protocol}://github.com/commontk/PythonQt.git"
-      GIT_TAG "patched"
+      GIT_TAG "origin/patched"
       CMAKE_GENERATOR ${gen}
       BUILD_COMMAND ""
       CMAKE_ARGS

CMakeExternals/VTK.cmake

@@ -25,6 +25,7 @@ IF(${add_project})
 #     MESSAGE(STATUS "Adding project:${proj}")
     ExternalProject_Add(${proj}
       GIT_REPOSITORY ${git_protocol}://vtk.org/VTK.git
+      GIT_TAG "origin/master"
       INSTALL_COMMAND ""
       CMAKE_GENERATOR ${gen}
       CMAKE_ARGS

CMakeExternals/ZMQ.cmake

@@ -21,6 +21,7 @@ IF(${add_project})
   #   MESSAGE(STATUS "Adding project:${proj}")
     ExternalProject_Add(${proj}
       GIT_REPOSITORY ${git_protocol}://github.com/PatrickCheng/zeromq2.git
+      GIT_TAG "origin/master"
       INSTALL_COMMAND ""
       CMAKE_GENERATOR ${gen}
       CMAKE_ARGS