CmdLine: Provide better diagnostics on file conflict.

For #353.

Examples of new output:

**Conflict with CKAN module:**

```
$ ./ckan.exe install ModuleConflictor
About to install...

 * ModuleConflictor 2.5.1 (cached)

Continue? [Y/N]


Installing mod "ModuleConflictor 2.5.1"

Oh no! We tried to overwrite a file owned by another mod!
Please try a `ckan update` and try again.

If this problem re-occurs, then it maybe a packaging bug.
Please report it at:

https://github.com/KSP-CKAN/CKAN-meta/issues/new

Please including the following information in your report:

File           : GameData/ModuleManager.2.5.1.dll
Installing Mod : ModuleConflictor 2.5.1
Owning Mod     : ModuleManager
CKAN Version   : v1.1.0-RC1-4-gdb3a7a3 (unstable)

Your GameData has been returned to its original state.
```

**Conflict with pre-existing module:**

```
$ ./ckan.exe install TweakScale
About to install...

 * TweakScale v1.44 (cached)

Continue? [Y/N]


Installing mod "TweakScale v1.44"


Oh no!

It looks like you're trying to install a mod which is already installed,
or which conflicts with another mod which is already installed.

As a safety feature, the CKAN will *never* overwrite or alter a file
that it did not install itself.

If you wish to install TweakScale v1.44 via the CKAN,
then please manually uninstall the mod which owns:

GameData/TweakScale/B9_TweakScale.cfg

and try again.

Your GameData has been returned to its original state.
```