More robust curl downloads

[ViralBShah]

Can we pass some extra parameters to curl so that it can retry downloads after disconnects?

MESSAGE: Changing Directory to /Users/viral/.julia/Cairo/deps/builds/fontconfig-2.10.2
MESSAGE: Changing Directory to /Users/viral/.julia/Cairo/deps/builds/fontconfig-2.10.2
MESSAGE: Changing Directory to /Users/viral/.julia/Cairo/deps/builds/fontconfig-2.10.2
MESSAGE: Attempting to Create directory /Users/viral/.julia/Cairo/deps/downloads
MESSAGE: Directory /Users/viral/.julia/Cairo/deps/downloads already created
MESSAGE: Downloading file http://www.cairographics.org/releases/cairo-1.12.8.tar.xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0Bus error: 10
 87 40.1M   87 35.2M    0     0  61392      0  0:11:25  0:10:02  0:01:23 71599
curl: (18) transfer closed with 5118218 bytes remaining to read

In case of incomplete downloads, BinDeps should remove the partial download. Running the buildscript gives the following error:

julia> Pkg.runbuildscript("Cairo")
MESSAGE: Running build script for package Cairo
/Users/viral/.julia/Cairo/deps
MESSAGE: There are multiple options available for installing this dependency:
- skip: Skip Installation - Binaries must be installed manually
- brew: Install depdendency using brew
- source: Install depdendency from source
Plese select desired method: source
MESSAGE: Changing Directory to /Users/viral/.julia/Cairo/deps
<cut>

MESSAGE: Attempting to Create directory /Users/viral/.julia/Cairo/deps/downloads
MESSAGE: Directory /Users/viral/.julia/Cairo/deps/downloads already created
MESSAGE: Attempting to Create directory /Users/viral/.julia/Cairo/deps/downloads
MESSAGE: Directory /Users/viral/.julia/Cairo/deps/downloads already created
MESSAGE: Downloading file http://www.cairographics.org/releases/cairo-1.12.8.tar.xz
MESSAGE: Done downloading file http://www.cairographics.org/releases/cairo-1.12.8.tar.xz
MESSAGE: Attempting to Create directory /Users/viral/.julia/Cairo/deps/src
MESSAGE: Directory /Users/viral/.julia/Cairo/deps/src already created
MESSAGE: Attempting to Create directory /Users/viral/.julia/Cairo/deps/src/cairo-1.12.8
ERROR: in spawn: new not defined
 in spawn at process.jl:240
 in run at process.jl:377
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:359
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:376
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:376
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:376
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:147
 in run at /Users/viral/.julia/BinDeps/src/BinDeps.jl:376
 in include_from_node1 at loading.jl:76
 in anonymous at no file:206
 in cd at file.jl:26
 in runbuildscript at pkg.jl:203
at /Users/viral/.julia/Cairo/deps/build.jl:79

julia> 

[mlubin]

This would be addressed by properly implementing #21.

[Keno]

Closing in favor of #21.