Certain valid characters in refs aren't being escaped properly

[mistydemeo]

Certain valid characters in git branch names aren't being escaped properly, leading to a failure to fetch them. A good example is #, which will obviously break API calls if passed through without escaping.

This was broken by #1006. URI::Parser handles this correctly, escaping # to %23, while Addressable::URI leaves it as #. Versions of Octokit from 4.9.0 to current git HEAD are affected.

Steps to reproduce:

1. Create and push up a branch named foo#bar
2. Using Octokit, run client.branch("myrepo", "foo#bar")

Expected results:

Octokit fetches the branch and returns metadata.

Actual results:

Octokit returns a 404.

[indigok]

I double checked this using curl and got the same results, so it looks like it might be a problem with the API itself.

For example, trying

curl -H "Authorization: token $GITHUB_TOKEN" https://api.github.com/repos/octopup/api-sandbox/branches/test#this

returns:

{
  "message": "Branch not found",
  "documentation_url": "https://developer.github.com/v3/repos/branches/#get-branch"
}

Although I can see the branch test#this under curl -H "Authorization: token $GITHUB_TOKEN" https://api.github.com/repos/octopup/api-sandbox/branches and the other branches like master work as expected.

Additionally, escaping it directly works as expected:

curl -H "Authorization: token $GITHUB_TOKEN" https://api.github.com/repos/octopup/api-sandbox/branches/test%23this

[mistydemeo]

@hmharvey I believe that's expected. Because of how URL routing works, anything past a literal # doesn't make its way into the server to the app. # always needs to be encoded in order to be used in URLs like this.