[REG 4.5 -> 4.6] Which files are shown by git commit editor depends on the project's name

1. Start creating a new Qt Widgets Application project with the name "gitProject".
2. On the last page of the wizard, select "Git" as version control system.
3. Select "Tools" -> "Git" -> "Local Repository" -> "Commit" from the menu.
   The project's .pro.user file is being shown as untracked file which can be committed:
   
   When the project has a different name, the .pro.user file will not be shown.

It usually will not make much sense to commit the .pro.user file into git. What is even worse is, that it depends on the name of the project which files will be shown.

This did not happen with Creator 4.5.

Found and tested by Squish test tst_git_local.

43f57d3f31117c7677d23f1477a4579b1b562c67 is the first bad commit
commit 43f57d3f31117c7677d23f1477a4579b1b562c67
Author: Tobias Hunger <tobias.hunger@qt.io>
Date:   Mon Dec 4 12:58:10 2017 +0100

    Session: Get rid of cache of all project file names

    Make the project responsible to provide information on which files
    belong to it instead.

    Change-Id: I80accf9104af33eaffc6b8f3e6024e9725697d37
    Reviewed-by: Eike Ziller <eike.ziller@qt.io>