Basic dependency checking. setup() has two new optional arguments

requires and provides. requires is a sequence of strings, of the
form 'packagename-version'. The dependency checking so far merely
does an '__import__(packagename)' and checks for packagename.__version__
You can also leave off the version, and any version of the package
will be installed.
There's a special case for the package 'python' - sys.version_info
is used, so
requires= ( 'python-2.3', )
just works.

Provides is of the same format as requires - but if it's not supplied,
a provides is generated by adding the version to each entry in packages,
or modules if packages isn't there.
Provides is currently only used in the PKG-INFO file. Shortly, PyPI
will grow the ability to accept these lines, and register will be
updated to send them.

There's a new command 'checkdep' command that runs these checks.
For this version, only greater-than-or-equal checking is done. We'll
add the ability to specify an optional operator later.

Lib/distutils/command/__init__.py

@@ -24,6 +24,7 @@ __all__ = ['build',
            'bdist_dumb',
            'bdist_rpm',
            'bdist_wininst',
+           'checkdep',
            # These two are reserved for future use:
            #'bdist_sdux',
            #'bdist_pkgtool',