sack: hif_sack_evr_cpm does not require sack
sack: hif_sack_evr_cpm does not require sack

the pools which are used in `pool_evrcmp_str` could never
differ from any hawkey sacks so we create an ad hoc one.
`pool_evrcmp_str` looks for `pool.havedistroepoch` and
`pool.promoteepoch` attributes which are not set anywhere
in libhif. It's still better to use for comparison one source
(libsolv) then call the other implementation from rpm.

Closes: #126
Approved by: cgwalters

Conan-Kudo/libhif,Conan-Kudo/libhif,hughsie/libhif,edynox/libdnf,edynox/libdnf,Conan-Kudo/libhif,Conan-Kudo/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,rpm-software-management/libhif,hughsie/libhif,edynox/libdnf,rpm-software-management/libdnf,hughsie/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,rpm-software-management/libhif,hughsie/libhif,edynox/libdnf,rpm-software-management/libdnf