Cleanup Net::LDAP::Connection#search arg handling
Skip fixture add if exists

This can happen if a failure prevents this from being cleaned
up properly in the last run.
Include required search base, fix test DN
Document search args with relevant RFC sections
Merge pull request #139 from ruby-ldap/search-connection-cleanup

Net::LDAP::Connection#search cleanup
Merge branch 'master' into open-integration-tests

Conflicts:
	lib/net/ldap/connection.rb
	test/test_ldap_connection.rb
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