Return partial shadow information to non-root users

This also returns everything except the password hash from the shadow
database to non-root users (nothing was returned before). This allows
non-root users to do PAM authentication in some configurations.

On some systems there is a setgid executable that is allowed to read
/etc/shadow for authentication by e.g. screensavers. Returning no shadow
information will cause pam_unix to deny authorisation in common
configurations.

See:
http://bugs.debian.org/706913
Implement function for resetting reconnect times

This implemens a myldap_immediate_reconnect() function that resets the
reconnect timer to retry failing connections to the LDAP server upon the
next search.

This can be used to cut the reconnect_sleeptime and reconnect_retrytime
sleeping periodss short if we have some indication that the LDAP server
is available again.
Handle SIGUSR1 by resetting the retry timer

This implements and documents handling of the SIGUSR1 signal in nslcd to
reset the reconnect_sleeptime and reconnect_retrytime timers to re-check
availability of the LDAP server.
Retry LDAP servers quickly after receiving SIGUSR1

When nslcd receives the SIGUSR1 signal it will retry connecting to
unavailable LDAP servers sooner.

This signal can for example be sent when (re)stablishing a network
connection.
Have pynslcd handle mapped userPassword

This fixes an error that could occur when the userPassword was retrieved
from LDAP and insufficient privileges were available for reading the
attribute.