Simplify git_describe to work on CMake 2.8.0.

FindGit doesn't seem to work as expected on Ubuntu 10.04
(GIT-NOTFOUND even though Git is installed and available
on the $PATH).

This implementation might be overly simplistic and it
should probably use find_program() to locate Git. We need
to revisit this after the 0.12.0 release is out.

Author: dnadlinger

cmake/Modules/GetGitRevisionDescription.cmake

@@ -74,33 +74,10 @@ function(get_git_head_revision _refspecvar _hashvar)
 endfunction()
 
 function(git_describe _var)
-	if(NOT GIT_FOUND)
-		find_package(Git QUIET)
-	endif()
-	get_git_head_revision(refspec hash)
-	if(NOT GIT_FOUND)
-		set(${_var} "GIT-NOTFOUND" PARENT_SCOPE)
-		return()
-	endif()
-	if(NOT hash)
-		set(${_var} "HEAD-HASH-NOTFOUND" PARENT_SCOPE)
-		return()
-	endif()
-
-	# TODO sanitize
-	#if((${ARGN}" MATCHES "&&") OR
-	#	(ARGN MATCHES "||") OR
-	#	(ARGN MATCHES "\\;"))
-	#	message("Please report the following error to the project!")
-	#	message(FATAL_ERROR "Looks like someone's doing something nefarious with git_describe! Passed arguments ${ARGN}")
-	#endif()
-
-	#message(STATUS "Arguments to execute_process: ${ARGN}")
-
 	execute_process(COMMAND
-		"${GIT_EXECUTABLE}"
+		git
 		describe
-		${hash}
+		HEAD
 		${ARGN}
 		WORKING_DIRECTORY
 		"${CMAKE_SOURCE_DIR}"