do not use sed for version date processing but rather cut and tr

Based on an idea from Karel Gardas, who had troubles with the original
sed version (which didn't work with /usr/bin/sed on Solaris).

aclocal.m4

@@ -1116,7 +1116,7 @@ if test "$RELEASE" = "NO"; then
         AC_MSG_RESULT(given $PACKAGE_VERSION)
     elif test -d .git; then
         changequote(, )dnl
-        ver_date=`git log -n 1 --date=short --pretty=format:%ci | sed "s/^.*\([0-9][0-9][0-9][0-9]\)-\([0-9][0-9]\)-\([0-9][0-9]\).*$/\1\2\3/"`
+        ver_date=`git log -n 1 --date=short --pretty=format:%ci | cut -d ' ' -f 1 | tr -d -`
         if echo $ver_date | grep '^[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]$' 2>&1 >/dev/null; then true; else
         changequote([, ])dnl
                 AC_MSG_ERROR([failed to detect version date: check that git is in your path])