Provide some vars for use in template's targets.

These new vars are DESTDIR (by default XBPS_DESTDIR/pkgname-version),
SRCPKGDESTDIR (XBPS_DESTDIR/sourcepkg-version) and FILESDIR
(XBPS_TEMPLATESDIR/pkgname/files).

This simplifies packages that used them.

--HG--
extra : convert_revision : 287ea7128cb5df19870ca7aff0a3b8f99a11d63a

templates/shadow/template

@@ -33,11 +33,9 @@ pre_build()
 
 post_install()
 {
-	local destdir=$XBPS_DESTDIR/$pkgname-$version
-
 	# Use the same auth file for all these cmds.
 	for f in chpasswd chgpasswd groupadd groupdel groupmems \
 		 groupmod newusers useradd userdel usermod other; do
-		install -m644 $destdir/etc/pam.d/chage $destdir/etc/pam.d/${f}
+		install -m644 $DESTDIR/etc/pam.d/chage $DESTDIR/etc/pam.d/${f}
 	done
 }