sh/init.sh.Linux.in: update test for live /proc to use md5sum

This allows us to avoid the warnings from bash-4.4 about null bytes in
command substitutions.

If you have separate /usr, are not using an initramfs, and have a file
called /proc/self/environ on your root file system, this will break.
X-Gentoo-Bug: 594534
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=594534

sh/init.sh.Linux.in

@@ -21,7 +21,7 @@ fi
 mountproc=true
 f=/proc/self/environ
 if [ -e $f ]; then
-	if [ "$(VAR=a cat $f)" = "$(VAR=b cat $f)" ]; then
+	if [ "$(VAR=a md5sum $f)" = "$(VAR=b md5sum $f)" ]; then
 		eerror "You have cruft in /proc that should be deleted"
 	else
 		einfo "/proc is already mounted"