Fix scriptdir/bindir

[dhoegh]

When I tried to update JuliaLang/IJulia.jl#357 to use the bindir and scriptdir function I found that the function pointed to the wrong scripts/bins. The scripts within the pkgs cannot be used because they cannot find the python interpreter. On Linux the Ipython script in deps/usr/bin works as intended and it looks like:

#!/home/hoegh/anaconda3/bin/python3
if __name__ == '__main__':
    import sys
    from IPython import start_ipython

    sys.exit(start_ipython())

the equivalent script in deps/usr/bin/pkgs/ipython-3.1.0-py34_0/bin do not work because it cannot find the python interpreter referenced in the first line.

#!/opt/anaconda1anaconda2anaconda3/bin/python3
if __name__ == '__main__':
    import sys
    from IPython import start_ipython

    sys.exit(start_ipython())

The case is the same on windows where executables inside deps\usr\pkgs do not work, while the equivalent executable in deps\usr\Scripts work. Therefore this PR update's to use the global bin directory on Linux and Scripts directory windows in deps/usr/. As bindir/scriptdir is not package dependent anymore I have made them constants and capitalized.

[dhoegh]

The old equivalent to this would be @test v"4.0.0"==run($(joinpath(Conda.scriptsdir(), "jypyter")) kernelspec --version) which would fail because the script do not work.

[dhoegh]

The old equivalent to this was @test v"4.0.0" == convert(VersionNumber, chomp(readall($(joinpath(Conda.scriptsdir("jupyter"), "jupyter")) kernelspec --version))) which would fail because the script did not work.

[dhoegh]

The old equivalent to this was @test v"4.0.0" == convert(VersionNumber, chomp(readall($(joinpath(Conda.scriptsdir("jupyter"), "jupyter-kernelspec")) --version))) which would fail because the script did not work.

[Luthaf]

Thank you for that, it is nice of you !

Can you just update the documentation, and squash your commits ?

[dhoegh]

I have change the documentation to match. Are there any further changes to the documentation you see necerssary?

[Luthaf]

Are there any further changes to the documentation you see necerssary?

No, sorry, I was tired ... Thank you again !