tests: removed Python 2.6 from Travis CI config

Missing _bsddb in Travis CI's Python 2.6 environment causes build
failure at the present time.
reliability: reconstructing URL base path in SRU WSGI application
bugfix: fixed IndexError when Workflows log a zero-length message

e.g. <log></log>
bugfix: fixed bug in ResultSet ordering by XPath
style: incremented version numbers
docs: updated CHANGES file
Merge branch 'hotfix/1.0.12'
Merge tag '1.0.12' into develop

finished bugfix release 1.0.12