mvparent: fix moving several dirs with relative paths

Moving several directories with relative paths did not work because the
script was not going back to its original working directory.

file_utils/mvparent.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# mvparent.sh, Copyright © 2007, 2010 Matteo Cypriani
+# mvparent.sh, Copyright © 2007, 2010, 2020 Matteo Cypriani
 #
 # This program is free software. It comes without any warranty, to
 # the extent permitted by applicable law. You can redistribute it
@@ -49,6 +49,7 @@ while [ -n "$1" ] ; do
     fi
 
     rmdir "$target"
+    cd "$OLDPWD"
 done
 
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