Set sourcepkg to pkgname through run_template().

This removes the need for having to specify sourcepkg manually in
every package that will build subpkgs.

--HG--
extra : convert_revision : 383e4c467e84844d2f4f61ae5c5e07a5124e9cfb

templates/lcms/template

@@ -1,6 +1,5 @@
 # Template build file for 'lcms'.
 pkgname=lcms
-sourcepkg=$pkgname
 version=1.18a
 wrksrc=${pkgname}-${version%[a-z]*}
 distfiles="http://www.littlecms.com/$pkgname-$version.tar.gz"