Upgrade contextlib2 to 0.5.1
Upgrade contextlib2 to 0.5.1

alex/warehouse,pypa/warehouse,alex/warehouse,pypa/warehouse,dstufft/warehouse,pypa/warehouse,karan/warehouse,wlonk/warehouse,karan/warehouse,alex/warehouse,wlonk/warehouse,karan/warehouse,alex/warehouse,karan/warehouse,dstufft/warehouse,karan/warehouse,alex/warehouse,pypa/warehouse,dstufft/warehouse,wlonk/warehouse,dstufft/warehouse