Fix "kpm pack" paths with dots excluding all content files

When fixing #588 , I added `@"**\.*\**"` as a `pack-exclude` pattern. However, the pattern was translated to the following regex
```
^.*\.[^\\]*(\\)?\\.*$
```
, which means, all paths containing dots will be excluded. So if your project has a name containing one or more dots, for example `Microsoft.AspNet.SignalR.LoadTestHarness`, all files in this project will be excluded during packing.

Thanks @mikary for reporting this bug. I fixed it by adding proper directory separators when translating patterns to regex. Tested on both Windows and OSX.