Change `MainProject()` logic to skip over non-GitHub remotes

When running `hub pull-request` with this git remote setup:
* origin:   `github.com/myuser/myfork`
* github:   `github.com/owner/repo`
* upstream: `example.com/other-repo`

this error would be shown:

    Aborted: the origin remote doesn't point to a GitHub repository.

The error is both unfortunate (the existence of "upstream" shouldn't
have aborted the whole operation) and misleading (it wasn't the "origin"
remote that was the problem).

This changes `MainProject()` so it skips over non-GitHub remotes until
it finds one that points to a GitHub project.

features/ci_status.feature

@@ -85,7 +85,10 @@ Feature: hub ci-status
   Scenario: Non-GitHub repo
     Given the "origin" remote has url "mygh:Manganeez/repo.git"
     When I run `hub ci-status`
-    Then the stderr should contain "Aborted: the origin remote doesn't point to a GitHub repository.\n"
+    Then the stderr should contain exactly:
+      """
+      Aborted: could not find any git remote pointing to a GitHub repository\n
+      """
     And the exit status should be 1
 
   Scenario: Enterprise CI statuses

features/compare.feature

@@ -152,7 +152,7 @@ Feature: hub compare
     Then the stdout should contain exactly ""
     And the stderr should contain exactly:
       """
-      Aborted: the origin remote doesn't point to a GitHub repository.\n
+      Aborted: could not find any git remote pointing to a GitHub repository\n
       """
     And the exit status should be 1
 

features/fork.feature

@@ -250,7 +250,7 @@ Feature: hub fork
     Then the exit status should be 1
     And the stderr should contain exactly:
       """
-      Aborted: the origin remote doesn't point to a GitHub repository.\n
+      Aborted: could not find any git remote pointing to a GitHub repository\n
       """
     And there should be no "origin" remote
 
@@ -260,7 +260,7 @@ Feature: hub fork
     Then the exit status should be 1
     And the stderr should contain exactly:
       """
-      Aborted: the origin remote doesn't point to a GitHub repository.\n
+      Aborted: could not find any git remote pointing to a GitHub repository\n
       """
 
   Scenario: Enterprise fork

features/pull_request.feature

@@ -13,7 +13,10 @@ Feature: hub pull-request
   Scenario: Non-GitHub repo
     Given the "origin" remote has url "mygh:Manganeez/repo.git"
     When I run `hub pull-request`
-    Then the stderr should contain "Aborted: the origin remote doesn't point to a GitHub repository.\n"
+    Then the stderr should contain exactly:
+      """
+      Aborted: could not find any git remote pointing to a GitHub repository\n
+      """
     And the exit status should be 1
 
   Scenario: Create pull request respecting "insteadOf" configuration
@@ -822,6 +825,23 @@ Feature: hub pull-request
     When I successfully run `hub pull-request -m hereyougo`
     Then the output should contain exactly "the://url\n"
 
+  Scenario: Create pull request to "github" remote when "upstream" is non-GitHub
+    Given I am on the "master" branch pushed to "origin/master"
+    And the "github" remote has url "git://github.com/github/coral.git"
+    And the "upstream" remote has url "git://example.com/coral.git"
+    Given the GitHub API server:
+      """
+      post('/repos/github/coral/pulls') {
+        assert :base  => 'master',
+               :head  => 'mislav:master',
+               :title => 'hereyougo'
+        status 201
+        json :html_url => "the://url"
+      }
+      """
+    When I successfully run `hub pull-request -m hereyougo`
+    Then the output should contain exactly "the://url\n"
+
   Scenario: Open pull request in web browser
     Given the GitHub API server:
       """

github/localrepo.go

@@ -192,34 +192,25 @@ func (r *GitHubRepo) RemoteForProject(project *Project) (*Remote, error) {
 	return nil, fmt.Errorf("could not find a git remote for '%s'", project)
 }
 
-func (r *GitHubRepo) MainRemote() (remote *Remote, err error) {
+func (r *GitHubRepo) MainRemote() (*Remote, error) {
 	r.loadRemotes()
 
 	if len(r.remotes) > 0 {
-		remote = &r.remotes[0]
-	}
-
-	if remote == nil {
-		err = fmt.Errorf("Can't find git remote origin")
+		return &r.remotes[0], nil
+	} else {
+		return nil, fmt.Errorf("no git remotes found")
 	}
-
-	return
 }
 
-func (r *GitHubRepo) MainProject() (project *Project, err error) {
-	origin, err := r.MainRemote()
-	if err != nil {
-		err = fmt.Errorf("Aborted: the origin remote doesn't point to a GitHub repository.")
-
-		return
-	}
+func (r *GitHubRepo) MainProject() (*Project, error) {
+	r.loadRemotes()
 
-	project, err = origin.Project()
-	if err != nil {
-		err = fmt.Errorf("Aborted: the origin remote doesn't point to a GitHub repository.")
+	for _, remote := range r.remotes {
+		if project, err := remote.Project(); err == nil {
+			return project, nil
+		}
 	}
-
-	return
+	return nil, fmt.Errorf("Aborted: could not find any git remote pointing to a GitHub repository")
 }
 
 func (r *GitHubRepo) CurrentProject() (project *Project, err error) {