add Debian which but call it witch instead

sh/witch

@@ -0,0 +1,66 @@
+#!/usr/bin/env sh
+# this is `which` from Debian. the only changes are superficial (formatting).
+# this does not work as-is with zsh.
+
+set -ef
+
+if test -n "$KSH_VERSION"; then
+	puts() {
+		print -r -- "$*"
+	}
+else
+	puts() {
+		printf '%s\n' "$*"
+	}
+fi
+
+ALLMATCHES=0
+
+while getopts a whichopts
+do
+	case "$whichopts" in
+		a) ALLMATCHES=1 ;;
+		?) puts "Usage: $0 [-a] args"; exit 2 ;;
+	esac
+done
+shift $(($OPTIND - 1))
+
+if [ "$#" -eq 0 ]; then
+	ALLRET=1
+else
+	ALLRET=0
+fi
+case $PATH in
+	(*[!:]:) PATH="$PATH:" ;;
+esac
+for PROGRAM in "$@"; do
+	RET=1
+	IFS_SAVE="$IFS"
+	IFS=:
+	case $PROGRAM in
+		*/*)
+			if [ -f "$PROGRAM" ] && [ -x "$PROGRAM" ]; then
+				puts "$PROGRAM"
+				RET=0
+			fi
+			;;
+		*)
+			for ELEMENT in $PATH; do
+				if [ -z "$ELEMENT" ]; then
+					ELEMENT=.
+				fi
+				if [ -f "$ELEMENT/$PROGRAM" ] && [ -x "$ELEMENT/$PROGRAM" ]; then
+					puts "$ELEMENT/$PROGRAM"
+					RET=0
+					[ "$ALLMATCHES" -eq 1 ] || break
+				fi
+			done
+			;;
+	esac
+	IFS="$IFS_SAVE"
+	if [ "$RET" -ne 0 ]; then
+		ALLRET=1
+	fi
+done
+
+exit "$ALLRET"