fix zfec to install under 2.4

[zooko]

• fix zfec to install under 2.4 (the relative ..util in cmdline.zfec breaks byte-compilation)

"cmdline" isn't used by tahoe, so maybe I can configure GNUmakefile to configure setup.py to not try to compile cmdline.

[warner]

the zfec setup.py will need to refrain from putting the cmdline/*.py modules into any generated distributions (like the 'install' target), because it's the deban package's post-install script that tries to byte-compile every .py in the bundle and fails on the 2.5-only syntax

To retain the 2.5-only relative imports, you might have setup.py do something like:

packages = ['zfec', 'zfec.util', 'zfec.test']
if sys.version_info[0:2] >= (2.5):
   packages += ['zfec.cmdline']

setup(
...
    package=packages,
...
)

Or, by renaming cmdline/zfec.py to something that doesn't overlap with the top-level zfec/ package (say cmdline_zfec.py), you could use absolute imports and make even the command-line tools work under 2.4.