net.lo: Add the ability to find the full path of a binary

Some of the networking tools, such as iproute2, can be stored in one of
several locations. This function gives us a standard way to find these
tools.

I would like to thankRobin Johnson <robbat2@gentoo.org> for his input on
this function.

init.d/net.lo.in

@@ -169,6 +169,18 @@ _configure_variables()
 	done
 }
 
+_which()
+{
+	local i OIFS
+	[ -z "$1" ] && return
+	OIFS="$IFS"
+	IFS=:
+	for i in $PATH ; do
+		[ -x $i/$1 ] && echo $i/$1 && break
+	done
+	IFS=$OIFS
+}
+
 _show_address()
 {
 	einfo "received address $(_get_inet_address "${IFACE}")"