Add python-lxml to ubuntu-precise; resolves travis-ci/apt-package-whitelist#2338
Add python-lxml to ubuntu-precise; resolves travis-ci/apt-package-whitelist#2338

Packages: python-lxml python-lxml-dbg python3-lxml python3-lxml-dbg python-lxml-doc

travis-ci/apt-package-whitelist,travis-ci/apt-package-whitelist