`using PyPlot` fails

Something in the past few weeks has made PyPlot unusable. I'm on PyCall v0.4.5, PyPlot v1.2.5, and PySide v0.0.2.

in the julia terminal:

```
julia> using PyPlot
ERROR: PyError (PyImport_ImportModule)
in pyerr_check at /Users/joshua/.julia/PyCall/src/exception.jl:58
in pyimport at /Users/joshua/.julia/PyCall/src/PyCall.jl:85
in pyinitialize at /Users/joshua/.julia/PyCall/src/PyCall.jl:259
in pyinitialize at /Users/joshua/.julia/PyCall/src/PyCall.jl:447
in pyimport at /Users/joshua/.julia/PyCall/src/PyCall.jl:105
in reload_path at loading.jl:152
in _require at loading.jl:67
in require at loading.jl:51SYSTEM: show(lasterr) caused an error
```

in Ijulia:

```
In[*]: using PyPlot
KERNEL EXCEPTION
access to undefined reference
in convert at /Users/joshua/.julia/PyCall/src/conversions.jl:82
in pystring at /Users/joshua/.julia/PyCall/src/PyCall.jl:542
in show at /Users/joshua/.julia/PyCall/src/exception.jl:35
in showerror at replutil.jl:66
in showerror at replutil.jl:74 (repeats 2 times)
in showerror at replutil.jl:72
in sprint at io.jl:460
in pyerr_content at /Users/joshua/.julia/IJulia/src/execute_request.jl:66
```

```
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| | |_| | | | (_| | | Version 0.3.0-prerelease+2570 (2014-04-09 19:29 UTC)
_/ |\__'_|_|_|__'_| | Commit 4fc2a15 (34 days old master)
|__/ | x86_64-apple-darwin13.1.0

Reproduce `using PyPlot` in Julia 0.3.0 with PyCall v0.4.5, PyPlot v1.2.5, and PySide v0.0.2, starting with the terminal traceback. Read the referenced PyCall files—src/exception.jl, src/PyCall.jl, and src/conversions.jl—and the IJulia execute_request.jl path; done means PyPlot imports without the reported PyError or kernel exception.

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