finish port to julia 0.6

[bjarthur]

this simply adds one more commit to #239 which removes the remaining dep warns. one can now cleanly using Compose on julia 0.5 and 0.6.

while tests pass on 0.6, they currently don't for 0.5, neither for the master branch of Compose nor this PR:

julia> Pkg.test("Compose")
INFO: Computing test dependencies for Compose...
INFO: No packages to install, update or remove
INFO: Testing Compose
Test Failed
  Expression: ((text_extents(font_family,8pt,"test test"))[1])[2] * 2 == ((text_extents(font_family,8pt,"test\ntest"))[1])[2]
   Evaluated: 3.7758246527777772mm == 5.206917317708333mm

but that is a separate issue...

[bjarthur]

tests pass on 0.5 and nightly. will merge in a couple days unless someone has a concern.

the text_extents failure mentioned above appears to be something peculiar to my local machine. i also experience another failure locally involving small differences in the generated .svg files which have no impact on the visual appearance. but travis is happy, so so am i.

[tlnagy]

@bjarthur Thanks for taking the time to update my PR. I'm working on getting Measures.jl working right now. It looks like we're closing in on getting the Gadfly stack onto 0.6! 🎉

[tlnagy]

Also, the text_extents failures could be due to you having slightly different fonts being used then the Travis Linux boxes.

[bjarthur]

i've got measures working already. just need to push the PR

[tlnagy]

Ah. Well I have PR here: JuliaGraphics/Measures.jl#12 waiting for it to pass tests.