libopkg: pkg_hash: print unresolved dependencies

libopkg: pkg_hash: print unresolved dependencies

When a package is not installed because it has unresolved dependencies
normally we get only an error message like this:
 * pkg_hash_fetch_best_installation_candidate: Packages for ltq-vdsl-app found, but incompatible with the architectures configured
 * opkg_install_cmd: Cannot install package ltq-vdsl-app.

Log in addition the following error message:
 * pkg_hash_check_unresolved: cannot find dependency ltq-dsl-base for ltq-vdsl-app

Fixes: FS#3814
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>