Enables mssql support (#383)

* Enables mssql support

Port of dlobs work in gogs.
Enables options in index.js
Enables MSSQL as a database option in go.
Sets ID to 0 on initial migration. Required for
MSSQL insert statements.

Signed-off-by: Beau Trepp <beautrepp@gmail.com>

* Vendors in denisenkom/go-mssqldb

Includes golang.org/x/crypto/md4
as this is required by go-msssqldb

Signed-off-by: Beau Trepp <beautrepp@gmail.com>

modules/setting/setting.go

@@ -100,6 +100,7 @@ var (
 	// Database settings
 	UseSQLite3    bool
 	UseMySQL      bool
+	UseMSSQL      bool
 	UsePostgreSQL bool
 	UseTiDB       bool