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/enchant/template

@@ -1,6 +1,5 @@
 # Template file for 'enchant'
 pkgname=enchant
-sourcepkg=$pkgname
 version=1.4.2
 distfiles="http://www.abisource.com/downloads/enchant/$version/enchant-$version.tar.gz"
 build_style=gnu_configure