Paket pack skips files #2445

Description

Starting from 5.0.0-rc009 paket skips duplicate files from the package being created.

Repro steps

1. Create a Test.template file like this:

type file
id Paket.Test
version 1.0.0
description Paket Test
authors NK
files
    File1.txt ==> tools\Dir1
    File1.txt ==> tools\Dir2

2. Run .\paket.exe pack output . templatefile .\Test.template

Expected behavior

The resulting package should contain both directories with File1.txt in each of them.
A real-life scenario is when a package contains multiple applications sharing some common libraries.

Actual behavior

The resulting package only contains Dir1.

Known workarounds

None.