Remove python 2.5'isms

Remove python 2.5'isms

The following python 2.5 features were worked around:

    * the sha module is used as a fallback when the hashlib module is
      not available
    * the 'any' built-in method was replaced with a 'for' loop
    * a conditional expression was replaced with an 'if' statement
    * the subprocess.check_call method was replaced by a call to
      subprocess.Popen followed by a call to subprocess.wait with a
      check of its return status

These changes allow the python infrastructure to be used with python 2.4
which is distributed with RedHat's RHEL 5, for example.

t5800 was updated to check for python >= 2.4 to reflect these changes.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>