Introduce install/remove iterators.

These iterator constructors lets you pass in two sets and creates
an iterator for the packages to remove or the packages to install.
The iterators will step through the packages in a sequence that respects
the pre, post, preun and postun modifiers.

Right now, the install order isn't actually implemented, this patch just
implements the API changes and updates the applications.

 prefix=@prefix@

 exec_prefix=@exec_prefix@

 libdir=@libdir@

 includedir=@includedir@

 Name: razor

 Description: library for depsolving, installing and removing packages

 Version: @VERSION@

 Requires: expat curl

 Libs: -L${libdir} -lexpat -lz -lcurl

 Cflags: -I${includedir}/razor