pkg: Reinstate one-to-many mapping from RPMs to Debs

Signed-off-by: Euan Harris <euan.harris@citrix.com>
pkg: Move RPM to Deb name mapping out of library

Signed-off-by: Euan Harris <euan.harris@citrix.com>
pkg: Strip RPM 4.6's architecture annotations from 'Provides'

Signed-off-by: Euan Harris <euan.harris@citrix.com>
pkg: Make 'dist' a parameter of Spec constructor

Signed-off-by: Euan Harris <euan.harris@citrix.com>