RT#77716: LDAP.pm: new option keepalive for new()

If given, set the socket's SO_KEEPALIVE option depending on the
boolean value of the option's value.
Filter.pm: new method negate()

In-place negate [=apply the logic operation NOT] the filter object.
Filter.pod: fix/clarify documentation of new() and parse()
{Cancel,Refresh}.pm: fix typo in documentation
Search.pod: clarify zero-based counting in entry()
Control/Paged.pm: document that it only applies to search requests
Util.pm: new function ldap_url_parse()
Control/ProxyAuth.pm: fix typo in documentation
LDAP.pm: convert scheme to lowercase in new()

Increase compatibility with URI.pm and allow URLs to be passed
with schemes in mixed/upper case too.
Constant.pm: Add Active Directory capability constants
FAQ.pod: add examples for nested group searches
FAQ.pod: add example to search all members of a large group
t/7{1pre,2post}read.t: don't use deprecated methods

Use Net::LDAP::Entry->get_value instead of the deprecated get_attrbute
to avoid a deprecation warning in the tests.
Merge pull request #17 from marschap/next

preparation for the next release