Find the system's MD5 binary.

Different binaries calculate MD5 checksums on different systems. Try
a couple known programs and only calculate and verify the checksum
if they exist. This should silence warnings on eg OpenBSD.

hgeditor

@@ -1,54 +1,56 b''
 #!/bin/sh
 #
 # This is an example of using HGEDITOR to create of diff to review the
 # changes while commiting.
 
 # If you want to pass your favourite editor some other parameters
 # only for Mercurial, modify this:
 case "${EDITOR}" in
     "")
         EDITOR="vi"
         ;;
     emacs)
         EDITOR="$EDITOR -nw"
         ;;
     gvim|vim)
         EDITOR="$EDITOR -f -o"
         ;;
 esac
 
 
 HGTMP=""
 cleanup_exit() {
     rm -rf "$HGTMP"
 }
 
 # Remove temporary files even if we get interrupted
 trap "cleanup_exit" 0 # normal exit
 trap "exit 255" 1 2 3 6 15 # HUP INT QUIT ABRT TERM
 
 HGTMP="${TMPDIR-/tmp}/hgeditor.$RANDOM.$RANDOM.$RANDOM.$$"
 (umask 077 && mkdir "$HGTMP") || {
     echo "Could not create temporary directory! Exiting." 1>&2
     exit 1
 }
 
 (
     grep '^HG: changed' "$1" | cut -b 13- | while read changed; do
         hg diff "$changed" >> "$HGTMP/diff"
     done
 )
 
 cat "$1" > "$HGTMP/msg"
 
-CHECKSUM=`md5sum "$HGTMP/msg"`
+MD5=$(which md5sum 2>/dev/null) || \
+    MD5=$(which md5 2>/dev/null) 
+[ -x "${MD5}" ] && CHECKSUM=`${MD5} "$HGTMP/msg"`
 if [ -s "$HGTMP/diff" ]; then
     $EDITOR "$HGTMP/msg" "$HGTMP/diff" || exit $?
 else
     $EDITOR "$HGTMP/msg" || exit $?
 fi
-echo "$CHECKSUM" | md5sum -c >/dev/null 2>&1 && exit 13
+[ -x "${MD5}" ] && (echo "$CHECKSUM" | ${MD5} -c >/dev/null 2>&1 && exit 13)
 
 mv "$HGTMP/msg" "$1"
 
 exit $?