Fix sortgroup function

This fixes an issue with the sortgroup function which failed to handle a
group line with only two colons correctly. Such group entries have been
seen in the wild on FreeBSD.

Also, comment lines in group files are now ignored (also seen on
FreeBSD).
Provide a script for setting up slapd

The setup_slapd.sh script can be used to set up and start a slapd
instance in a single (temporary) directory. The slapd instance is
configured and loaded with test data for use in the test environment.
Update tests README

This refreshes the documentation of the tests, especially the test
environment.
Remove unnecessary attributes from test.ldif
Make script to check test environment

This changes the in_testenv.sh script into testenv.sh which has more
checks and a few functions to configure the test environment.
Handle other responses in test_pamcmds

This extends test_pamcmds to handle other pam/su/passwd errors and
responses (as seen on CentOS 5). Also switch to stronger password when
changing the test user's password to avoid problems with password
strength checks.
Improve portability of ldap test

This supports old ldapsearch commands that don't support the -x and -H
options and ldapsearch commands that don't exit with a failure code if
nothing is found.

This also switches the test_myldap test to use the testenv check for the
LDAP server.