Fix `hub pr list -h <BRANCH>` when owner isn't specified

Previously, when `:` wouldn't appear in the value for `head`, the GitHub
API would ignore the `head` parameter altogether. Now, ensure that
`<OWNER>:` syntax is always populated by adding the default from the
current repository.

commands/pr.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strconv"
+	"strings"
 
 	"github.com/github/hub/github"
 	"github.com/github/hub/ui"
@@ -32,8 +33,9 @@ pr checkout <PR-NUMBER> [<BRANCH>]
 	-s, --state <STATE>
 		Filter pull requests by <STATE> (default: "open").
 
-	-h, --head <BRANCH>
-		Show pull requests started from the specified head <BRANCH>.
+	-h, --head [<OWNER>:]<BRANCH>
+		Show pull requests started from the specified head <BRANCH>. The default
+		value for <OWNER> is taken from the current repository.
 
 	-b, --base <BRANCH>
 		Show pull requests based on the specified <BRANCH>.
@@ -162,6 +164,10 @@ func listPulls(cmd *Command, args *Args) {
 		return
 	}
 
+	if flagPullRequestHead != "" && !strings.Contains(flagPullRequestHead, ":") {
+		flagPullRequestHead = fmt.Sprintf("%s:%s", project.Owner, flagPullRequestHead)
+	}
+
 	flagFilters := map[string]string{
 		"state": flagPullRequestState,
 		"head":  flagPullRequestHead,

features/pr-list.feature

@@ -81,10 +81,22 @@ Feature: hub pr list
     """
     get('/repos/github/hub/pulls') {
       assert :base => "develop",
-             :head => "patch-1"
+             :head => "github:patch-1"
 
       json []
     }
     """
     When I successfully run `hub pr list -b develop -h patch-1`
     Then the output should contain exactly ""
+
+  Scenario: Filter by head with owner
+    Given the GitHub API server:
+    """
+    get('/repos/github/hub/pulls') {
+      assert :head => "mislav:patch-1"
+
+      json []
+    }
+    """
+    When I successfully run `hub pr list -h mislav:patch-1`
+    Then the output should contain exactly ""