seperate ssh constants from schema constants

The contants were placed in the same section as the scheme ones, which
may lead to confusion.

modules/setting/setting.go

@@ -27,14 +27,17 @@ import (
 	"github.com/gogits/gogs/modules/user"
 )
 
+const (
+	SSH_PUBLICKEY_CHECK_NATIVE = "native"
+	SSH_PUBLICKEY_CHECK_KEYGEN = "ssh-keygen"
+)
+
 type Scheme string
 
 const (
 	HTTP  Scheme = "http"
 	HTTPS Scheme = "https"
 	FCGI  Scheme = "fcgi"
-	SSH_PUBLICKEY_CHECK_NATIVE        = "native"
-	SSH_PUBLICKEY_CHECK_KEYGEN        = "ssh-keygen"
 )
 
 type LandingPage string