py-ldap: updated to 3.1.0

Released 3.1.0:

This release brings two minor API changes:
- Long-deprecated functions ldap.open() and ldap.init() are removed
- LDAPObject.compare_s() and compare_ext_s return bool instead of 0 or 1

All changes since 3.0.0:

Lib/
* Remove long deprecated functions ldap.open() and ldap.init()
* LDAPObject.compare_s() and LDAPObject.compare_ext_s() now return a bool
  instead of 1 or 0.
* Make iteration over cidict yield same values as keys()
* Fail if pyasn1 is not installed
* Fix parsing of PPolicyControl ASN.1 structure
* Use items() when appropriate in dict iteration
* Add support for tracing LDAP calls. Tracing can now be enabled with
  the env var PYTHON_LDAP_TRACE_LEVEL and redirected to a file with
  PYTHON_LDAP_TRACE_FILE.
  (This is mainly intended for debugging and internal testing; the
  configuration or output may change in future versions.)

Modules/
* Fix ref counting bug in LDAPmessage_to_python

Doc/
* Remove warning about unreleased version
* Doc: Replace Mac OS X -> macOS

Tests/
* Add tests and coverage for tracing
* Disable warnings-as-errors for Python 3.4
* Fix assertTrue to assertEqual
* Mark several test values as bytes

Lib/slapdtest/
* Fix error message for missing commands
* Make SlapdObject a context manager
* Disable SASL external when missing SASL support
* Make SlapdObject.root_dn a property
* In SlapdObject, build include directives dynamically
* Move import statements to top level

Code style:
* Add Makefile rules for automatic formatting of C and Python code
* Reformat and indent all C files
* Trim white space throughout the project

Infrastructure:
* Add py3-trace tox environment to Travis CI config
* Add new Pytest cache directory to gitignore

General:
* Update all pypi.python.org URLs to pypi.org

Released 3.0.0:

Notable changes since 2.4.45 (please see detailed logs below):
* Python 3 support and bytes_mode
  see: https://python-ldap.readthedocs.io/en/latest/bytes_mode.html
* The module ldap.async is renamed to ldap.asyncsearch
* New dependencies: pyasn1, pyasn1_modules
* Dropped support for Python 2.6 and 3.3

(adam)