note duplicated gitrev build process

pkg/gitrev.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 # Usage: gitrev.sh path-to-src
 
+# This script generates the header with git revision information
+# NOTE: Changes made here must also be made in SConstruct!
 REVID=`git rev-parse HEAD`;
 export FULLTAG=`git tag --sort=v:refname | tail -n1`;
 TAGREV=`git rev-parse $FULLTAG`;