build: make git submodule checking more reliable

* cfg.mk (_curr_status): Accommodate leading "+" or "-" in the output
of git submodule status.
* autogen.sh: Likewise.

autogen.sh

@@ -65,7 +65,7 @@ fi
 # Ensure that whenever we pull in a gnulib update or otherwise change to a
 # different version (i.e., when switching branches), we also rerun ./bootstrap.
 curr_status=.git-module-status
-t=$(git submodule status)
+t=$(git submodule status|sed 's/^[ +-]//;s/ .*//')
 if test "$t" = "$(cat $curr_status 2>/dev/null)"; then
     : # good, it's up to date, all we need is autoreconf
     autoreconf -if

cfg.mk

@@ -262,7 +262,9 @@ ifeq (0,$(MAKELEVEL))
   # submodule name.  Contrast these:
   # -b653eda3ac4864de205419d9f41eec267cb89eeb .gnulib
   #  b653eda3ac4864de205419d9f41eec267cb89eeb .gnulib (v0.0-2286-gb653eda)
-  _submodule_hash = sed 's/.//;s/ .*//'
+  # $ cat .git-module-status
+  # b653eda3ac4864de205419d9f41eec267cb89eeb
+  _submodule_hash = sed 's/^[ +-]//;s/ .*//'
   _update_required := $(shell						\
       actual=$$(git submodule status | $(_submodule_hash));		\
       stamp="$$($(_submodule_hash) $(_curr_status) 2>/dev/null)";	\