RFE: Extend repodata format for PreRequires

Description of problem:
The current repodata format limits the PreRequires to the "legacy" 
pre-requires which are written like this in a spec file:

PreReq: foo

Autodetected install or erase requires (Requires(post) and 
Requires(preun)) as well as the manual written
   Requires(pre): foo
   Requires(post): foo
   Requires(preun): foo
   Requires(postun): foo
are ignored by createrepo and yum at the moment.

The following extention to the repodata format would allow those 
prerequires to be honored and used as well:

Add a 'type' property to the rpm:entry for requires which can have a 
combination of the following values:

   'legacy': The ones that are currently supported
   'pre': The Requires(pre) prereqs
   'post': The Requires(post) prereqs
   'preun': The Requires(preun) prereqs
   'postun': The Requires(postun) prereqs

For multiple entries in a single prereq the values could be separated by 
a "," to define a list of prereq types.

If 'type' is missing but 'pre' is set to '1' then 'legacy' is assumed 
which would allow 100% compatibility with the old repodata format.

The general benefit would be that by including these prereqs the 
repodata could be used to do complete depresolving and especially 
ordering without any real rpm headers.

For a quick test of the idea here the steps to look into:

1. Grab all requires form current rpms.
2. Detect all forms of prereqs and install and erase loops
3. Try to break those loops without the pre, post, preun and postun 
prereqs can result in wrong ordering

Read ya, Phil

-- 
Philipp Knirsch      | Tel.:  +49-711-96437-470
Development          | Fax.:  +49-711-96437-111
Red Hat GmbH         | Email: Phil Knirsch <[email protected]>
Hauptstaetterstr. 58 | Web:   http://www.redhat.de/
D-70178 Stuttgart
Motd:  You're only jealous cos the little penguins are talking to me.