Do not run conda install automagically (unless Conda.jl is used)

[tkf]

fix #560

[stevengj]

The error message should also suggest that the user run \"$aconda install -y $condapkg\" manually

[tkf]

I did that below. Isn't it enough?:

PyCall.jl/src/PyCall.jl

Lines 680 to 681 in f1def60

	To install $condapkg using $aconda, you can run the following command from your system shell:
	$aconda install$options $condapkg

[stevengj]

This is the case where it should say that PyCall was configured to use $python and suggest configuring with Conda.jl if the user wants automatic installation.

[tkf]

With #579 merged this rethrow() should show the detailed error message from pyimport:

PyCall.jl/src/PyCall.jl

Lines 461 to 482 in c45a076

	msg = msg * """
	PyCall is currently configured to use the Python version at:
	$python
	and you should use whatever mechanism you usually use (apt-get, pip, conda,
	etcetera) to install the Python package containing the $name module.
	One alternative is to re-configure PyCall to use a different Python
	version on your system: set ENV["PYTHON"] to the path/name of the python
	executable you want to use, run Pkg.build("PyCall"), and re-launch Julia.
	Another alternative is to configure PyCall to use a Julia-specific Python
	distribution via the Conda.jl package (which installs a private Anaconda
	Python distribution), which has the advantage that packages can be installed
	and kept up-to-date via Julia. As explained in the PyCall documentation,
	set ENV["PYTHON"]="", run Pkg.build("PyCall"), and re-launch Julia. Then,
	To install the $name module, you can use `pyimport_conda("$(escape_string(name))", PKG)`,
	where PKG is the Anaconda package the contains the module $name,
	or alternatively you can use the Conda package directly (via
	`using Conda` followed by `Conda.add` etcetera).
	"""

I guess it covers what you are saying?