Close #169. Renamed MOOSE_VERSION to _MOOSE_VERSION.

Since only developers uses it, it is safe to leave it undocumented in
CMakeLists.txt.

This variable is automatically set by git when building from git
repisitory. When git is not found, then one needs to pass this
information from command line.

This may break the build in `moose-package` repository in future.

Linux builds are safe on Open Build Service since cmake available on
those platforms are now new enough.

Author: Dilawar Singh

CMakeLists.txt

@@ -20,27 +20,27 @@ include(FindPkgConfig)
 set(VERSION_FILE ${CMAKE_CURRENT_SOURCE_DIR}/VERSION)
 find_program(GIT_EXEC "git")
 message( STATUS "Looking for git ${GIT_EXEC}" )
-if( (NOT __VERSION__) AND GIT_EXEC)
+if( (NOT _MOOSE_VERSION) AND GIT_EXEC)
     execute_process( 
         COMMAND ${GIT_EXEC} describe --tags --long
         WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-        OUTPUT_VARIABLE __VERSION__
+        OUTPUT_VARIABLE _MOOSE_VERSION
         OUTPUT_STRIP_TRAILING_WHITESPACE
         )
-    message(STATUS "+ Writing ${__VERSION__} to ${VERSION_FILE}" )
-    file(WRITE ${VERSION_FILE} ${__VERSION__})
-elseif( (NOT __VERSION__) AND (NOT GIT_EXEC) )
+    message(STATUS "+ Writing ${_MOOSE_VERSION} to ${VERSION_FILE}" )
+    file(WRITE ${VERSION_FILE} ${_MOOSE_VERSION})
+elseif( (NOT _MOOSE_VERSION) AND (NOT GIT_EXEC) )
     message(STATUS "+ Reading ${VERSION_FILE}" )
     file(READ ${VERSION_FILE} GIT_VERSION_OUTPUT )
-elseif(__VERSION__)
-    message(STATUS "+ Using user specified VERSION = ${__VERSION__}" )
-    file(WRITE ${VERSION_FILE} ${__VERSION__})
+elseif(_MOOSE_VERSION)
+    message(STATUS "+ Using user specified VERSION = ${_MOOSE_VERSION}" )
+    file(WRITE ${VERSION_FILE} ${_MOOSE_VERSION})
 else()
-    message(FATAL_ERROR "Could not determine __VERSION__" )
+    message(FATAL_ERROR "Could not determine _MOOSE_VERSION" )
 endif( )
 
-add_definitions( -D__VERSION__="${__VERSION__}")
-message( STATUS "MOOSE Version ${__VERSION__}" )
+add_definitions( -DMOOSE_VERSION="${_MOOSE_VERSION}")
+message( STATUS "MOOSE Version ${_MOOSE_VERSION}" )
 
 # This snippet is from LLVM project.
 # Sanity check our source directory to make sure that we are not trying to