PyPlot needs to be reinstalled after Julia is interrupted

Hello,

I have Julia 1.2.0 installed with Plots. For installing PyPlot backend without manually installing Python, I followed the instructions in [https://github.com/JuliaPy/PyPlot.jl](url) and did:

`ENV["PYTHON"]=""`
`Pkg.build("PyCall")`
`Pkg.add("PyPlot")`
`using Plots`
`pyplot()`

Then, everything went fine. However, if I interrupt Julia (not with Ctrl+C, but, e.g., when the light suddenly turns off and the computer suddenly shuts down), when I execute Julia again, I receive the following message:

`error compiling __init__: could not load library "/tmp/lib/libpython3.7m.so.1.0"
/tmp/lib/libpython3.7m.so.1.0: cannot open shared object file: No such file or directory`

and I have to reinstall PyPlot with the commands above.

I have the same problem in two computers (one uses Debian Stretch, the other uses Ubuntu).

The report centers on ENV["PYTHON"], Pkg.build("PyCall"), Pkg.add("PyPlot"), and pyplot() after an abrupt Julia shutdown; start by reproducing the restart failure on Julia 1.2.0 with the listed Debian or Ubuntu setup. Done means PyPlot initializes after restart without reinstalling, but no source files or tests are named.

Scritto dal modello di indicizzazione a partire dal testo della issue.