main/paxmark: validate and sort xattr flags

pax allows each letter to be in the xattr value only once, so
create the value accordingly. This also keeps the letters sorted
in the xattr value which is useful for apk in various ways.

main/paxmark/APKBUILD

 # Maintainer: Timo Teräs <timo.teras@iki.fi>
 pkgname=paxmark
-pkgver=0.5
+pkgver=0.6
 pkgrel=0
 pkgdesc="Manage PaX marking of executables"
 url="http://alpinelinux.org"
@@ -22,6 +22,6 @@ package() {
 	ln -s paxmark "$pkgdir"/usr/sbin/paxmark.sh || return 1
 }
 
-md5sums="08027e79219ed9b6d0e851e70dfa5f87  paxmark"
-sha256sums="be68fcf5ac7a84586e9201f0cca977d8cd4f824058f94b5b89e55f8c3f97711c  paxmark"
-sha512sums="346119a2cc675eb55440057a83fa9aba7a88bfd5bcc851b7ece34f60fbf5836e984f12af30894da3c795a02639ba189f730d403ef669457048c9777e0b2aaeca  paxmark"
+md5sums="363ee24e0f8eba76033e27d8ddca4e57  paxmark"
+sha256sums="1a2c0275f908d5011d4227dcc04eb32c53c63f2a6ce98f6fae0376e4c5e86c83  paxmark"
+sha512sums="eaa0a5cc11d3101df075a5291b14fa4865d959ce580f45e2b898be99397d6956aa1e34809a115d1a8ff7b7cc18abdc29cdf2ed36fdbd01c94500a05d248a5291  paxmark"

main/paxmark/paxmark

@@ -14,10 +14,21 @@ for f in "$@"; do
 done
 
 # Create XATTR_PAX marking using attr
-flags="${flags//z}"
-[ -n "${flags//[!Ee]}" ] || flags="${flags}e"
+local xval=""
+[ "${flags//[!P]}" ] && xval="${xval}P"
+[ "${flags//[!p]}" -a -z "${flags//[!P]}" ] && xval="${xval}p"
+[ "${flags//[!E]}" ] && xval="${xval}E"
+[ "${flags//[!e]}" -a -z "${flags//[!E]}" ] && xval="${xval}e"
+[ -z "${flags//[!Ee]}" ] && xval="${xval}e"
+[ "${flags//[!M]}" ] && xval="${xval}M"
+[ "${flags//[!m]}" -a -z "${flags//[!M]}" ] && xval="${xval}m"
+[ "${flags//[!R]}" ] && xval="${xval}R"
+[ "${flags//[!r]}" -a -z "${flags//[!R]}" ] && xval="${xval}r"
+[ "${flags//[!S]}" ] && xval="${xval}S"
+[ "${flags//[!s]}" -a -z "${flags//[!S]}" ] && xval="${xval}s"
+
 for f in "$@"; do
-	attr -q -s pax.flags -V "${flags}" "${f}" >/dev/null 2>&1 && continue
+	attr -q -s pax.flags -V "${xval}" "${f}" >/dev/null 2>&1 && continue
 	ret=1
 done