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/sed.tmpl

@@ -1,7 +1,7 @@
 # Template file for 'sed'
 pkgname=sed
 version=4.1.5
-distfiles="http://ftp.gnu.org/gnu/$pkgname/$pkgname-$version@.tar.gz"
+distfiles="http://ftp.gnu.org/gnu/$pkgname/$pkgname-$version.tar.gz"
 build_style=gnu_configure
 configure_args="--bindir=$XBPS_DESTDIR/$pkgname-$version/bin"
 short_desc="The GNU stream editor"