Fix version string

The previous version was hardcoded in the script, and not linked to Git
tags. It has been 1.0 since Dec 24 15:35:32 2012, before the 1.0.0 tag
actually.

Makefile

@@ -7,6 +7,7 @@ ifndef SHELL_PATH
 endif
 
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
+GIT_LATEXDIFF_VERSION=${shell git describe --tags HEAD}
 gitexecdir_SQ = $(subst ','\'',$(gitexecdir))
 
 SCRIPT=git-latexdiff
@@ -19,5 +20,7 @@ help:
 	@echo 'Run "$(MAKE) install" to install $(SCRIPT) in gitexecdir.'
 
 install:
-	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' $(SCRIPT) > '$(gitexecdir_SQ)/$(SCRIPT)'
+	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
+	    -e 's|@GIT_LATEXDIFF_VERSION@|$(GIT_LATEXDIFF_VERSION)|' \
+	        $(SCRIPT) > '$(gitexecdir_SQ)/$(SCRIPT)'
 	chmod 755 '$(gitexecdir)/$(SCRIPT)'

git-latexdiff

@@ -41,7 +41,15 @@
 set -o errexit
 set -o noclobber
 
-git_latexdiff_version=1.0
+git_latexdiff_version='@GIT_LATEXDIFF_VERSION@'
+
+git_latexdiff_compute_version () {
+    if [ "$git_latexdiff_version" = '@GIT_LATEXDIFF_VERSION@' ]; then
+	(cd "$(dirname "$0")" && git describe --tags HEAD)
+    else
+	echo "$git_latexdiff_version"
+    fi
+}
 
 usage () {
     cat << EOF
@@ -223,7 +231,7 @@ while test $# -ne 0; do
 	    quiet=1
 	    ;;
 	"--version")
-	    echo "$git_latexdiff_version"
+	    git_latexdiff_compute_version
             exit 0
 	    ;;
 	"--subtree")