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>

vendor/github.com/denisenkom/go-mssqldb/rpc.go

@@ -0,0 +1,100 @@
+package mssql
+
+import (
+	"encoding/binary"
+)
+
+type ProcId struct {
+	id   uint16
+	name string
+}
+
+// parameter flags
+const (
+	fByRevValue   = 1
+	fDefaultValue = 2
+)
+
+type Param struct {
+	Name   string
+	Flags  uint8
+	ti     typeInfo
+	buffer []byte
+}
+
+func MakeProcId(name string) (res ProcId) {
+	res.name = name
+	if len(name) == 0 {
+		panic("Proc name shouln't be empty")
+	}
+	if len(name) >= 0xffff {
+		panic("Invalid length of procedure name, should be less than 0xffff")
+	}
+	return res
+}
+
+const (
+	fWithRecomp    = 1
+	fNoMetaData    = 2
+	fReuseMetaData = 4
+)
+
+var (
+	Sp_Cursor          = ProcId{1, ""}
+	Sp_CursorOpen      = ProcId{2, ""}
+	Sp_CursorPrepare   = ProcId{3, ""}
+	Sp_CursorExecute   = ProcId{4, ""}
+	Sp_CursorPrepExec  = ProcId{5, ""}
+	Sp_CursorUnprepare = ProcId{6, ""}
+	Sp_CursorFetch     = ProcId{7, ""}
+	Sp_CursorOption    = ProcId{8, ""}
+	Sp_CursorClose     = ProcId{9, ""}
+	Sp_ExecuteSql      = ProcId{10, ""}
+	Sp_Prepare         = ProcId{11, ""}
+	Sp_PrepExec        = ProcId{13, ""}
+	Sp_PrepExecRpc     = ProcId{14, ""}
+	Sp_Unprepare       = ProcId{15, ""}
+)
+
+// http://msdn.microsoft.com/en-us/library/dd357576.aspx
+func sendRpc(buf *tdsBuffer, headers []headerStruct, proc ProcId, flags uint16, params []Param) (err error) {
+	buf.BeginPacket(packRPCRequest)
+	writeAllHeaders(buf, headers)
+	if len(proc.name) == 0 {
+		var idswitch uint16 = 0xffff
+		err = binary.Write(buf, binary.LittleEndian, &idswitch)
+		if err != nil {
+			return
+		}
+		err = binary.Write(buf, binary.LittleEndian, &proc.id)
+		if err != nil {
+			return
+		}
+	} else {
+		err = writeUsVarChar(buf, proc.name)
+		if err != nil {
+			return
+		}
+	}
+	err = binary.Write(buf, binary.LittleEndian, &flags)
+	if err != nil {
+		return
+	}
+	for _, param := range params {
+		if err = writeBVarChar(buf, param.Name); err != nil {
+			return
+		}
+		if err = binary.Write(buf, binary.LittleEndian, param.Flags); err != nil {
+			return
+		}
+		err = writeTypeInfo(buf, &param.ti)
+		if err != nil {
+			return
+		}
+		err = param.ti.Writer(buf, param.ti, param.buffer)
+		if err != nil {
+			return
+		}
+	}
+	return buf.FinishPacket()
+}