Parse raised exceptions and their error messages sans interpolation/format spec

This PR partially addresses #3024. It also provides a shiny new script useful looking at the current state of the messages in raised exceptions. Here's an example of some output:

Example
=====
![pandas-shiny-new-parse-asserts](https://f.cloud.github.com/assets/417981/457480/70282b60-b39e-11e2-8db1-f5cfb4f0c5bf.png)

You can reproduce this with

```sh
scripts/parse_except.py --type empty --module pandas --kind assert
```
from the top level pandas directory.

Description
=======
The above line searches for all empty raises in the module `pandas` whose constructor matches the regular expression `'.*assert.*'`--not case sensitive.

Note: **This assumes you have installed pandas with `python setup.py develop`**. This will not work without that (well, that's not strictly true, but it will search for pandas code that's installed wherever you installed it `/usr/*/site-packages/*/pandas` or `$VIRTUAL_ENV/*/pandas`, for example, which is probably not what you want).

To see all of the options and a short description you can do the usual:
```sh
scripts/parse_except.py --help
```