Use bash features to improve $distfiles parsing.

That means that it's not necessary anymore to use an '@' before the
extract suffix string. yay.

--HG--
extra : convert_revision : 83ce2c783cb917ef59b87eacb0565cfcff277218

templates/mng.tmpl

@@ -2,7 +2,7 @@
 pkgname=mng
 version=1.0.10
 wrksrc="libmng-$version"
-distfiles="http://www.libmng.com/download/libmng-$version@.tar.bz2"
+distfiles="http://www.libmng.com/download/libmng-$version.tar.bz2"
 build_style=gnu_configure
 make_cmd="$XBPS_MASTERDIR/bin/gmake"
 short_desc="Multiple-image Network Graphics (MNG) reference library"