Store commit.Status as an enum instead of a string

This is unrelated to the changes in this PR, but since we are doing the same
thing for the commit.Action field in the next commit, it makes sense to do it
for Status too for consistency. Modelling this as an enum feels more natural
than modelling it as a string, since there's a finite set of possible values.
And it saves a little bit of memory (not very much, since none of the strings
were heap-allocated, but still).

pkg/commands/models/commit.go

@@ -9,11 +9,23 @@ import (
 // Special commit hash for empty tree object
 const EmptyTreeCommitHash = "4b825dc642cb6eb9a060e54bf8d69288fbee4904"
 
+type CommitStatus int
+
+const (
+	StatusNone CommitStatus = iota
+	StatusUnpushed
+	StatusPushed
+	StatusMerged
+	StatusRebasing
+	StatusSelected
+	StatusReflog
+)
+
 // Commit : A git commit
 type Commit struct {
 	Sha           string
 	Name          string
-	Status        string // one of "unpushed", "pushed", "merged", "rebasing" or "selected"
+	Status        CommitStatus
 	Action        string // one of "", "pick", "edit", "squash", "reword", "drop", "fixup"
 	Tags          []string
 	ExtraInfo     string // something like 'HEAD -> master, tag: v0.15.2'