disable Cython compilation in travis build

--HG--
extra : transplant_source : %C2%26%92L%E7%5Bt%8AF%94R%BC%28%F3%00%93%BB%F4%E5%DB
drop old pip option in travis build

--HG--
extra : transplant_source : %F6%C80q%F0%89%DE%99%BD6%9C%AE%26%DD%40EaQ%7B%99
merge lxml-3.4 branch into master