Add "provides" field in packages (which affect both runtime and buildtime deps).
It replaces all the occurences in the deptree before solving, actually
allowing to swap packages and provide virtuals. Along with a mechanism
for package rename #25.
The version inmemory is optimized, while the boltdb implementation is
not.
It returns a list of the same package but with all the versions present
in the db.
Unmarshalling needs well-defined structs, also swap pointers in few places where needed.
There are few more TODOS pending (like getting UpdatePackage fixed properly)
Fixes races conditions and make the DB Switchable. Also prepare inside
the CompilationSpec the tree of the deps to be built, and parallelize
only the building jobs.
Closes#7
Signed-off-by: Ettore Di Giacinto <mudler@gentoo.org>
