Print the names of the installed packages too

Allows to remove quickly any already installed package that has not been
completely specified from the list of packages to install.

This should make Yum invocations much shorter, often without any
"install" line at all.  It should also make the "spare_dependencies"
method much faster, since it will do much smaller queries.
Add a simulation of how to reduce transactions
Detect when a desired package cannot be installed.

Yum only tells when a package cannot be installed with a tiny line in
stdout.  Look for that one.  Fixes #58.
Merge pull request #59 from piojo/spma-detect-missing-pkgs

Detect when a desired package cannot be installed.
Merge pull request #61 from piojo/smaller-transactions

Reduce the size of the transactions
ncm-metaconfig: add support for a preamble

Add support for including a preamble at the start of a file written by
ncm-metaconfig. This can be used to include contextual information in
the form of a comment since none of the modules supported by
ncm-metaconfig allow the insertion of comments into the files they
generate.
Merge pull request #62 from ned21/metaconfig-preamble

ncm-metaconfig: add support for a preamble