Use the contents of RELEASE as version fallback instead of 'UNKNOWN'

This makes binaries produced by source tarballs identify themselves with
the version number of the corresponding release series, unless overriden
by a 'VERSION' file.

RELEASE

@@ -0,0 +1 @@
+0.7

version.sh

@@ -5,7 +5,7 @@ revision=$(cd "$1" && git describe --always 2> /dev/null)
 test "$revision" && revision=git-$revision
 
 # no revision number found
-test "$revision" || revision=UNKNOWN
+test "$revision" || revision=$(cd "$1" && cat RELEASE 2> /dev/null)
 
 # releases extract the version number from the VERSION file
 version=$(cd "$1" && cat VERSION 2> /dev/null)