Cannot convert numbers to strings when reading an Excel spreadsheet
I'm reading some excel spreadsheets (xlsx format) into pandas using `read_excel`, which generally works great. The problem I have is that when a column contains numbers, pandas converts these to float64 type, and I would like them to be treated as strings. After reading them in, I can convert the column to str:

```
 my_frame.my_col = my_frame.my_col.astype('str') 
```

This works as far as assigning the right type to the column, but when I view the values in this column, the strings are formatted in scientific-format e.g. 8.027770e+14, which is not what I want. I like to be able to tell Pandas to read the columns as strings. My current solution involves dropping down to xlrd to read the spreadsheet.

See stackoverflow question: http://stackoverflow.com/q/20970483/690890
