Make: Move .tarball-version generation out of src/scripts/tarball

Commit 1ec9b94 made src/scripts/tarball generate .tarball-version and
.dirty-stamp.  Hardcoding it like that there is a bit ugly.

Move it into a separate tweak script that is run right before tar.
We'll tweak some more in the next commits.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

src/scripts/gen-tarball-version

@@ -0,0 +1,11 @@
+#!/bin/sh -e
+
+if [ $# = 0 ]; then
+    echo "Usage: $0 NAME VERSION (FILE | -C DIR)..."
+    exit 1
+fi
+
+nv=$1-$2
+
+printf "%s" "$2" >$nv/.tarball-version
+>$nv/.dirty-stamp

src/scripts/tarball

@@ -1,18 +1,23 @@
 #!/bin/sh -e
 
 if [ $# = 0 ]; then
-    echo "Usage: $0 NAME (FILE | -C DIR)..."
+    echo "Usage: $0 [-x TWEAK-SCRIPT ] NAME VERSION (FILE | -C DIR)..."
     exit 1
 fi
 
+script=:
+if [ "$1" == -x ]
+then
+    script=$2
+    shift; shift
+fi
+
 name="$1"
 version="$2"
 shift; shift
 
 nv=$name-$version
 mkdir $nv
-printf "%s" $version >$nv/.tarball-version
->$nv/.dirty-stamp
 
 # arrange cleanup
 trap 'rm -rf "$nv"' 0
@@ -30,4 +35,6 @@ until [ $# = 0 ]; do
     shift
 done
 
+$script $name $version
+
 tar -czf $nv.tar.gz --owner=0 --group=0 --mode=ug+w,a+rX $nv