Add a constructor and a SetTo() method with a
BPackageResolvableExpression parameter instead of a path. The path of
the package satisfying the expression is used.
The new functionality lives in libpackage as it uses the package kit.
* Add get_architecture(), get_primary_architecture(),
get_secondary_architectures(), guess_architecture_for_path() to get
the caller's architecture, the primary architecture, all secondary
architectures, or the architecture associated with a specified path
respectively.
* Rename the find_path*() functions to find_path*_etc() and add an
optional architecture parameter. Add simplified find_path*()
functions.
* BPathFinder: Add FindPath[s]() versions with an architecture
parameter.
