demo-treefile.json: Update for new syntax
treecompose: Fix use-before-alloc
doc: Add better treefile examples

These use inheritance now.
treecompose: Add missing space in subprocess printing
treecompose: Move yum repos out of the way *after* waiting for yum completion

Otherwise it just doesn't work.  Note this hack is only necessary for
the case where some package pulls in e.g. fedora-release in the
initial transaction set when we're trying to install nss-altfiles.