GeanyVC: Support for git worktree

[cas--]

I was using git-new-workdir and recently switched to using the newer form git worktree however found this stops the plugin working.

The reason appears to be that instead of a .git directory in the 'worktee directory' there is a .git file that contains a reference to the original directory. e.g. gitdir: /home/ubuntu/origdir.git/.git/worktrees/newdir.git.

[nomadbyte]

Here's a little test setup to formalize the use-case:

mkdir r1
cd r1

git init
git config user.name testuser
git config user.email testuser@
echo "f1" >> f1
git add f1
git commit -a -m "added f1"

git worktree add ../w1 -b work1
echo "f1:r1" >> f1
git status

cd ../w1
git status
echo "f2" >> f2
git add f2
git commit -a -m "added f2"
echo "f1:w1" >> f1
git status

Then in Geany, open both files: r1/f1 and w1/f1. Check:

1. The Version Control actions should be available for both files
2. Status for each of the f1 files should show the corresponding branch names (master, work1) and state: modified.
3. Diff for each file should list the respective changes (single line added f1:r1, f1:w1)
4. Commit dialog should list only one f1 file (per tree)
5. Commit should succeed for each of the trees
6. Final history for each file should list only tree-specific commits.

In the current Geany version (1.37), the step 1. above is failing for the w1/f1 file (worktree-based).