Merge branch 'jc/detached-head'

* jc/detached-head:
  git-checkout: handle local changes sanely when detaching HEAD
  git-checkout: safety check for detached HEAD checks existing refs
  git-checkout: fix branch name output from the command
  git-checkout: safety when coming back from the detached HEAD state.
  git-checkout: rewording comments regarding detached HEAD.
  git-checkout: do not warn detaching HEAD when it is already detached.
  Detached HEAD (experimental)
  git-branch: show detached HEAD
  git-status: show detached HEAD

path.c

@@ -90,10 +90,11 @@ int git_mkstemp(char *path, size_t len, const char *template)
 }
 
 
-int validate_symref(const char *path)
+int validate_headref(const char *path)
 {
 	struct stat st;
 	char *buf, buffer[256];
+	unsigned char sha1[20];
 	int len, fd;
 
 	if (lstat(path, &st) < 0)
@@ -119,14 +120,23 @@ int validate_symref(const char *path)
 	/*
 	 * Is it a symbolic ref?
 	 */
-	if (len < 4 || memcmp("ref:", buffer, 4))
+	if (len < 4)
 		return -1;
-	buf = buffer + 4;
-	len -= 4;
-	while (len && isspace(*buf))
-		buf++, len--;
-	if (len >= 5 && !memcmp("refs/", buf, 5))
+	if (!memcmp("ref:", buffer, 4)) {
+		buf = buffer + 4;
+		len -= 4;
+		while (len && isspace(*buf))
+			buf++, len--;
+		if (len >= 5 && !memcmp("refs/", buf, 5))
+			return 0;
+	}
+
+	/*
+	 * Is this a detached HEAD?
+	 */
+	if (!get_sha1_hex(buffer, sha1))
 		return 0;
+
 	return -1;
 }
 
@@ -241,7 +251,7 @@ char *enter_repo(char *path, int strict)
 		return NULL;
 
 	if (access("objects", X_OK) == 0 && access("refs", X_OK) == 0 &&
-	    validate_symref("HEAD") == 0) {
+	    validate_headref("HEAD") == 0) {
 		putenv("GIT_DIR=.");
 		check_repository_format();
 		return path;