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/cairo.tmpl

@@ -2,7 +2,7 @@
 pkgname=cairo
 version=1.7.6
 patch_files="$pkgname-doc-public-Makefile-in.diff"
-distfiles="http://cairographics.org/snapshots/$pkgname-$version@.tar.gz"
+distfiles="http://cairographics.org/snapshots/$pkgname-$version.tar.gz"
 build_style=gnu_configure
 make_cmd="$XBPS_MASTERDIR/bin/gmake"
 configure_args="--enable-glitz --enable-pdf --enable-ps"