better error message for loading 32-bit Python from 64-bit Julia

Executing

```
> using PyCall
> @pyimport math
```

within the Julia console interpreter crashes it immediately (i.e., makes the console quit and disappear immediately with no time to see any warnings or error messages).

Relevant software versions:
- OS: Windows 7
- julia: Version 0.3.8 (2015-04-30 23:40 UTC), x86_64-w64-mingw32
- PyCall: v0.8.1
- Python: Python 2.7.8 |Anaconda 2.1.0 (32-bit)| (default, Jul 2 2014, 15:13:35) [MSC v.1500 32 bit (Intel)] on win32

Start by reproducing the Julia console commands `using PyCall` and `@pyimport math` with the Windows, Julia, PyCall, and 32-bit Python versions listed. Trace PyCall's handling of Python startup and architecture mismatches; done means the console stays open and presents a clear error instead of exiting without a message.

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