Windows, fails to unpack

[SimonDanisch]

pkg> add PackageCompiler
┌ Info: Pkg3 is still under development, please file issues at `https://github.com/JuliaLang/Pkg3.jl`.
└ Pkg3 is running without precompile statements, first action will be slow.
[ Info: Resolving package versions
ERROR: Error when installing packages:
failed process: Process(`'C:\Users\sdani\AppData\Local\Julia-0.7.0-DEV\bin\7z.exe' x -si -y -ttar '-oC:\Users\sdani\AppData\Local\Temp\4quPbMZVkekT'`, ProcessExited(2)) [2]
Stacktrace:
 [1] error(::String, ::Base.Process, ::String, ::Int64, ::String) at .\error.jl:42
 [2] pipeline_error at .\process.jl:712 [inlined]
 [3] pipeline_error(::Base.ProcessChain) at .\process.jl:725
 [4] #run#537(::Bool, ::Function, ::Base.OrCmds, ::Tuple{Base.DevNullStream,Base.DevNullStream,Base.DevNullStream}, ::Vararg{Tuple{Base.DevNullStream,Base.DevNullStream,Base.DevNullStream},N} where N) at .\process.jl:670
 [5] run(::Base.OrCmds, ::Tuple{Base.DevNullStream,Base.DevNullStream,Base.DevNullStream}, ::Vararg{Tuple{Base.DevNullStream,Base.DevNullStream,Base.DevNullStream},N} where N) at .\process.jl:668
 [6] install_archive(::Array{String,1}, ::VersionNumber, ::String) at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\site\v0.7\Pkg3\src\Operations.jl:350
 [7] macro expansion at C:\cygwin\home\Administrator\buildbot\worker\package_win64\build\usr\share\julia\site\v0.7\Pkg3\src\Operations.jl:451 [inlined]
 [8] (::getfield(Pkg3.Operations, Symbol("##21#24")){Pkg3.Types.Context,Dict{Base.UUID,Array{String,1}}})() at .\event.jl:92

The file:

[SimonDanisch]

Other packages work, PackageCompiler even after deleting all Pkg3 folders, reproducably fails...

[KristofferC]

The offending package is indeed "BufferedStreams".

[KristofferC]

So the problem is that 7z on Windows chokes when trying to create the symlink at https://github.com/BioJulia/BufferedStreams.jl/blob/master/docs/src/index.md.

ERROR: Can not create symbolic link : A required privilege is not held by the client. : \BufferedStreams.jl-0.4.0\docs\index.md

We should fall back to LibGit2 if we fail to extract.

cc @bicycle1885

[KristofferC]

https://superuser.com/questions/1076527/7zip-cannot-create-symbolic-link-access-is-denied-to-libhdfs-so-and-libhadoop-s

https://superuser.com/questions/124679/how-do-i-create-a-link-in-windows-7-home-premium-as-a-regular-user/125981#125981

[bicycle1885]

This pull request may remove the problem: JuliaPackaging/WinRPM.jl#146.