Adds support for .gitignore at repository root

[osklyar]

This PR adds basic support for .gitignore files. The code uses github.com/monochromegane/go-gitignore, which, however, could be easily ported into a local package to avoid an additional external dependency.

The PR covers 99% of the normal .gitignore usage, however, the following limitations as compared to the standard git client exist:

• only .gitignore files at the root of the repository are considered, files located deeper in the tree structure are not taken into account
• files matching the exclusion pattern in the .gitignore will be considered not present on the file system, so if forcefully committed, they may be shown as a change (has not been investigated).

The effect of the change is easily seen in the following example using the go-git based client from github.com/silvertern/geat (WIP):

Older state, without the PR:

➜  geat git:(01172b3) geat status
.: [email protected]:silvertern/geat.git [origin] HEAD Changed
?? .idea/workspace.xml
?? .idea/geat.iml
?? .idea/modules.xml
?? .idea/vcs.xml
?? .idea/libraries/GOPATH__geat_.xml
?? .idea/misc.xml
?? vendor/github.com/caarlos0/spin/.gitignore
?? vendor/github.com/caarlos0/spin/.travis.yml
?? vendor/github.com/caarlos0/spin/README.md
?? vendor/github.com/caarlos0/spin/spin_test.go
?? vendor/github.com/caarlos0/spin/Makefile
?? vendor/github.com/caarlos0/spin/spin.go
?? Gopkg.lock

With the PR:

➜  geat git:(master) dep ensure
➜  geat git:(master) go install
➜  geat git:(master) geat status
.: [email protected]:silvertern/geat.git [origin] master Clean

➜  geat git:(master) echo "change" >> Gopkg.toml 
➜  geat git:(master) ✗ geat status                
.: [email protected]:silvertern/geat.git [origin] master Changed
 M Gopkg.toml

Addresses #307, #340

[alcortesm]

Please avoid adding content related to your choice of tools and editors to the project.

I suggest using a global $HOME/.gitignore file as an alternative.

git config --global core.excludesfile $HOME/.gitignore

[codecov]

Codecov Report

Merging #420 into master will decrease coverage by 0.61%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #420      +/-   ##
==========================================
- Coverage    77.8%   77.18%   -0.62%     
==========================================
  Files         124      124              
  Lines        9019     9020       +1     
==========================================
- Hits         7017     6962      -55     
- Misses       1229     1300      +71     
+ Partials      773      758      -15

Impacted Files	Coverage Δ
utils/merkletrie/filesystem/node.go	68.57% <100%> (+2.94%)	⬆️
plumbing/transport/ssh/common.go	0% <0%> (-50.91%)	⬇️
plumbing/transport/ssh/auth_method.go	33.33% <0%> (-24.77%)	⬇️
plumbing/transport/git/common.go	70.73% <0%> (-10.23%)	⬇️
remote.go	70.81% <0%> (-0.1%)	⬇️
plumbing/transport/file/client.go	100% <0%> (+6.25%)	⬆️

---

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[osklyar]

@alcortesm done, changes to .gitignore removed

[mcuadros]

Maybe the filesystem abstraction is not the best place for Implementing the .gitignore.
The right place IMHO is the Worktree, because in git you have some operations such as git add --force where the .gitignore is ignored. So you need to be aware of the ignored files at the Worktree level.

[osklyar]

@mcuadros The limitation has been listed in the original PR message, so it is a known limitation. I would generally agree with you for the change to be complete, but it would be much more involved and I would rather suggest doing it in a second iteration. I would not be able to offer a PR now for a change as suggested for the reasons of time constraints.

[mcuadros]

@osklyar what I am asking is for move this to Worktree, not about implement git add force. Otherwise we will need to redo this PR as soon as we need the force, or any other similar feature.

[osklyar]

@mcuadros Ok, fair enough. If it is more or less a move of the code I will investigate and try to provide the corresponding change.

[osklyar]

Ok, I now know how to introduce this change in the Worktree directly, however, I have found out that the third-party gitignore pattern matcher that I've been using the change is incorrect on some patterns. Therefore, I will close this PR, work on a change to have a clean pattern matcher in the Worktree and then submit a new one.