- To make future API changes easier, extended a class so that it is suitable
  for aptitude and to untie aptitude and libapt. (Aptitude depended on its
  details, because it reimplemented it.) (Picked from Debian apt 0.6.42.4.)
- Dropped a compat API, which could have still been relied on by libapt clients
  not aware of the support (since 0.5.15lorg2-alt73) for multiple hash types.

- Enabled the dialog to show changelogs. (In ALT, they are in the index,
  unlike in Debian, where they have to be downloaded separately.)
  Find it in the top menu: "Package" -> "Download Changelog". (TODO/patches
  are welcome: Place it along the package properties like dependencies.)

- Untied from the details of an interface in libapt by re-using a class from
  libapt (>= 0.5.15lorg2-alt86). (The dep was due to us reimplementing it.)

- Build PACKAGEKIT_1_2_5-30-g8957e9e49 with a fix for
  https://github.com/PackageKit/PackageKit/issues/539 (random crash).

- tests:
  + Enhanced to be able to work with test packages containing some files.
    (This will be useful for testing the work with large RPM archives.)
  + Shortened the run time of apt-xxtra-heavy-load-checkinstall.
  + Shortened the run time of other *-checkinstall scripts
    (by shortening the the test with zillion packages).

- Rewritten a tiny piece of code to fix build with lcc.
- Adapted to ALT's apt API a bit further by dropping an unused parameter of
  MarkInstall(). (In apt, it either has a default value or will be eliminated.)

- Implemented generic callback system for packagekit, allowing to show progress
  during offline-update to user. (Thx Oleg Solovyov mcpain@)

- Adapted to the new API with custom callbacks introduced
  in libapt-0.5.15lorg2-alt74. (Surprisingly, the call that had to be adapted
  is a method "private" to the apt library used here by means of a hack;
  so libapt shouldn't really bother to provide a compatibility method.)

- Show actual update percentage during offline update

- (tests) Report if a test (marked XFAIL) uneXpectedly passes (XPASS).
- (tests) Run them not in %check, but in *-checkinstall subpkgs. (To break
  build-dep cycle with apt-repo-tools, whose features are required by the tests,
  but which needs to be recompiled to be linked with libapt.)
- (tests) Done more extensive testing of how apt works with "rpm" repos
  via any of the file, http(s), cdrom methods; including:
  + re-fetching if the saved complete or partial pkglist indices are corrupt
    (see https://bugzilla.altlinux.org/show_bug.cgi?id=40746#c9 );
  + the verification of the checksums of pkglist indices. (The verification
    is tested in two ways:
    * The verification of the checksum of a specific type is tested by faking
      it in the meta-data: for MD5, SHA1, SHA256, BLAKE2b and just the size.
    * Simply testing that a faked pkglist file of the same size is rejected--no
      matter which hashing algorithm is used.)
  + the verification of the checksums of rpm archives. (The verification
    is tested in two ways:
    * The verification of the checksum of a specific type is tested by faking
      it in the meta-data: for MD5, SHA1, SHA256, BLAKE2b.
    * Simply testing that a faked rpm file of the same size is rejected--no
      matter which hashing algorithm is used.)
- (source code; ABI) Reverted a lot of inessential optimizations
  from 0.5.15lorg2-alt72.
- (source code; ABI) Got rid of virtual methods with default parameters
  (because they are confusing for the programmer).
- (source code; ABI) Backported some pieces of the support for the multiplicity
  of checksum (and compression) types from apt-rpm (thx imz@):
  + the type of the compression for "pkglist" indices;
  + the type of the checksum for "pkglist" indices;
  + the type of the checksum for "rpm" archives.
- Added blake2b hash support (thx glebfm@).
- Changed file and copy download methods to always compute checksums
  (thx glebfm@).

- Switched to librpm crypto API instead of libapt.
- Added support and enabled blake2b hash by default.
- genbasedir: add --disable-hash-caching option to disable hashsum caching.