Merge in the latest gnulib concat-filename module

diff --cc gl/modules/concat-filename
index 0000000000000000000000000000000000000000,9e86b793bfbaf3671b96ee1a00f1b8c45909f793..243eb7736912533e7a5a9801aafca6fa03582982
mode 000000,100644..100644
--- /dev/null
--- 2/gl/modules/concat-filename
+++ b/gl/modules/concat-filename
@@@ -1,0 -1,26 +1,24 @@@
 -malloc-posix
 -stpcpy
+ Description:
+ Construct a full filename by concatenating a directory name, a relative
+ filename, and a suffix.
+ 
+ Files:
+ lib/concat-filename.h
+ lib/concat-filename.c
+ 
+ Depends-on:
+ filename
+ 
+ configure.ac:
+ 
+ Makefile.am:
+ lib_SOURCES += concat-filename.c
+ 
+ Include:
+ "concat-filename.h"
+ 
+ License:
+ LGPLv2+
+ 
+ Maintainer:
+ all