Global Excludes .gitignore is not used

[Artemgy]

Release: Ubuntu 16.10
Package: qgit
Version: 2.6-1

When selecting files to include in a Commit, files are NOT excluded based on the Global Excludes list

## Steps to reproduce

* Create a global ignore file as per https://help.github.com/articles/ignoring-files/

$ cat >$HOME/.gitignore_global <<EOF!
#ghostwriter backup files
*.md.backup
EOF!
$ git config --global core.excludesfile ~/.gitignore_global

* Test the global setting from your local repo folder

$ cd my/repo/folder
$ touch help/use/markdown.md.backup
$ git check-ignore -v --no-index help/use/markdown.md.backup
/home/user/.gitignore_global:2:*.md.backup help/use/markdown.md.backup

* Open QGit
* Settings / Git Config shows the git options (both local and global) including
core.excludesfile = /home/user/.gitignore_global
* now Edit / Commit and you will see files with extension .md.backup appear in the Commit changes dialog
 - e.g. file: help/use/markdown.md.backup Index status: Not updated in index

## Workaround

* In EACH of your git local repo folders, execute the following

cat ~/.gitignore_global >> ./.git/info/exclude

Now Open QGit / Edit / Commit and you will see you files are ignored correctly

## Previous Research

I checked the launchpad bugs [https://bugs.launchpad.net/ubuntu/+source/qgit/]
the debian package bugs [https://bugs.debian.org/cgi-bin/pkgreport.cgi?pkg=qgit]
and upstream issues tracker [http://libre.tibirna.org/projects/qgit/issues]
but could not find anything similar mentioned there.