Add git commit version info

Makefile.am

@@ -1,3 +1,24 @@
 ACLOCAL_AMFLAGS = -I m4
 SUBDIRS = src scripts man conf
 EXTRA_DIST = autogen.sh ocb-license.html README.md COPYING.iOS
+nodist_noinst_HEADERS = version.h
+BUILT_SOURCES = version.h
+
+.PHONY:	VERSION
+
+VERSION:
+	@-[ -f VERSION ] || echo @PACKAGE_STRING@ > VERSION
+	@-git status > /dev/null 2>&1 && \
+		git describe --dirty > VERSION.new && \
+		! diff -q VERSION VERSION.new > /dev/null && \
+		mv VERSION.new VERSION
+	@rm -f VERSION.new
+
+version.h:	VERSION
+	@printf '#define BUILD_VERSION "%s"\n' "$$(cat VERSION)" > version.h.new
+	@-! diff -q version.h version.h.new > /dev/null && \
+		mv version.h.new version.h
+	@rm -f version.h.new
+
+clean-local:
+	@rm -f version.h VERSION