build_packages does not return a value any more. Code is really hacky
but works.

This is similar to the behaviour before the build number removal except
that it does not search recursively.

The build host should be an empty string for old packages.
"pisi li -b ''" now returns old packages, too.

This renamed parameter is used to filter packages by their build host.

  e.g. pisi li -b localhost

This can be changed using build_host option in pisi.conf. The
default value is "localhost". This can be used to distinguish
buildfarm packages and the packages built by the user.

Also store release numbers instead of build numbers.

The new format is:

    <name>-<source release>-<target release>-<distribution id>-<architecture>.delta.pisi

    e.g. pisi-179-180-p11-x86_64.pisi

Release numbers are used instead of build numbers.

This also adds utility functions to split fields of new filename format.

The new format is:

    <name>-<version>-<release>-<distribution id>-<architecture>.pisi

    e.g. pisi-2.3.2-180-p11-x86_64.pisi

We will not use build numbers any more. This commit removes some of the code
related to build numbers. New pisi will not deal with build numbers.
Before the stable release, all buildno-related code will be removed.

It is now possible to use digits after a dash character (e.g. polkit-qt-1).

Distribution id is a short string to represent the distribution release
(e.g. p11 for Pardus 2011).

Architecture strings cannot start with a digit. This is needed to
distinguish old and new packages.

Otherwise, the result of the test is dependent on the installed
packages.

No need to keep a member for source directory.

Also rename util.check_dir to util.ensure_dirs.

BUG:FIXED:14000

With this option, the compression type of index file can be selected.
It is possible to pass multiple types separated by comma.

e.g. pisi index --skip-signing --compression-types=bz2,xz

Now it signs all compressed index files and calculates sums
of them.

Also remove a redundant info message.

If defined, use WorkDir in actions.py. If it is not defined or the
directory does not exist, first try "srcname-version" then the
basename of archive URL after splitting extensions.