Duplicate files mentioned during discovery

* Populus Version: 1.11.2
* OS: linux

### What was wrong?
No error, but it's kind of a weird thing. I have my contracts in a hierarchical structure (1 level deep), and it looks something like:
```yaml
ico:
ICO.sol
Token.sol
utils:
Owned.sol
Haltable.sol
... # Others
... # Others
```
When I run `populus compile` I get the following feedback:
```bash
> Found 28 contract source files
- ico/ICO.sol
- ico/ICO.sol
- ico/Token.sol
- ico/Token.sol
- utils/Haltable.sol
- utils/Haltable.sol
- utils/Owned.sol
- utils/Owned.sol
- ... # Others
> Compiled 19 contracts
- ico/ICO.sol:ICO
- ico/Token.sol:Token
- utils/Haltable.sol:Haltable
- utils/Owned.sol:Owned
- ... # Others
> Wrote compiled assets to: build/contracts.json
```
In other words, it correctly compiles my contracts however it duplicates the discovery of my contract files which is weird. This probably has to do with my config file, which looks like:
```json
{
"version":"7",
"compilation":{
"contracts_source_dirs": [
"./",
"./utils"
"./ico",
"Other folders..."
],
"import_remappings": [
"utils=utils",
"ico=ico"
]
}
}
```
My project file is located at the base of my `contracts/` directory, and I run populus from there too.

EDIT: Removing the `./` from `contracts_source_dirs` list in my config file eliminated this issue. I still think it shouldn't be duplicating the discovery due to over-specifying my contract paths.