gnulib-tool feature request

[Sam Steingold]

Since I use gnulib in several sub-modules, I need to avoid conflicts between 
different gnulib imports.
thus I need to make all those _GL_* constants module-specific.
thus I need gnulib-tool to accept a --macro-prefix option and this patch:

iff --git a/gnulib-tool b/gnulib-tool
index ea451ec..6ed5e8e 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -2846,6 +2846,9 @@ s,^\(.................................................[^ 
]*\) *,
       break
     fi
   done
+  test -n ${macro_prefix} && sed_transform_lib_file=$sed_transform_lib_file"
+    s/_GL_/_${macro_prefix}_GL_/g
+  "
   sed_transform_main_lib_file="$sed_transform_lib_file"
   if test -n "$do_copyrights"; then
     if test -n "$lgpl"; then