import PyPlot fails

Hi,

I have problems importing PyPlot on different CentOS 7 and Fedora 20 machines:

```
julia> import PyPlot
Warning: error initializing module PyPlot:
PyCall.PyError(msg=":PyImport_ImportModule", T=PyCall.PyObject(o=0x0000000001d86520), val=PyCall.PyObject(o=0x000000000a5b1e18), traceback=PyCall.PyObject(o=0x0000000000000000))
```

Importing PyCall (only) works fine:

```
julia> import PyCall
julia> PyCall.pyinitialize()
```

Any idea how to fix the problem?

Regards,
Josef

No source file or test is identified. Start by reproducing `import PyPlot` on the reported CentOS 7 and Fedora 20 environments, then inspect the PyPlot and PyCall initialization paths and the existing issue discussion. Done means the initialization failure is explained and a verified fix or actionable diagnosis is available.

由索引模型根据 Issue 内容生成。