The warning message displayed only if it's a git repository that
has the following properties:
 - No remote.origin is set
 - it's NOT a git svn repo

This will prevent the message from being displayed when configuring Slicer:

CMake Warning at CMake/FindGit.cmake:108 (message):
  No remote origin set for git repository:
  /home/jchris/Projects/Slicer4/Extensions/CMake
Call Stack (most recent call first):
  CMake/SlicerMacroExtractRepositoryInfo.cmake:99 (GIT_WC_INFO)
  Extensions/CMake/CMakeLists.txt:73 (SlicerMacroExtractRepositoryInfo)

git-svn-id: http://svn.slicer.org/Slicer4/trunk@20577 3bd1e089-480b-0410-8dfb-8563597acbee