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/decimal.go

@@ -0,0 +1,115 @@
+package mssql
+
+import (
+	"encoding/binary"
+	"errors"
+	"math"
+	"math/big"
+)
+
+// http://msdn.microsoft.com/en-us/library/ee780893.aspx
+type Decimal struct {
+	integer  [4]uint32
+	positive bool
+	prec     uint8
+	scale    uint8
+}
+
+var scaletblflt64 [39]float64
+
+func (d Decimal) ToFloat64() float64 {
+	val := float64(0)
+	for i := 3; i >= 0; i-- {
+		val *= 0x100000000
+		val += float64(d.integer[i])
+	}
+	if !d.positive {
+		val = -val
+	}
+	if d.scale != 0 {
+		val /= scaletblflt64[d.scale]
+	}
+	return val
+}
+
+func Float64ToDecimal(f float64) (Decimal, error) {
+	var dec Decimal
+	if math.IsNaN(f) {
+		return dec, errors.New("NaN")
+	}
+	if math.IsInf(f, 0) {
+		return dec, errors.New("Infinity can't be converted to decimal")
+	}
+	dec.positive = f >= 0
+	if !dec.positive {
+		f = math.Abs(f)
+	}
+	if f > 3.402823669209385e+38 {
+		return dec, errors.New("Float value is out of range")
+	}
+	dec.prec = 20
+	var integer float64
+	for dec.scale = 0; dec.scale <= 20; dec.scale++ {
+		integer = f * scaletblflt64[dec.scale]
+		_, frac := math.Modf(integer)
+		if frac == 0 {
+			break
+		}
+	}
+	for i := 0; i < 4; i++ {
+		mod := math.Mod(integer, 0x100000000)
+		integer -= mod
+		integer /= 0x100000000
+		dec.integer[i] = uint32(mod)
+	}
+	return dec, nil
+}
+
+func init() {
+	var acc float64 = 1
+	for i := 0; i <= 38; i++ {
+		scaletblflt64[i] = acc
+		acc *= 10
+	}
+}
+
+func (d Decimal) Bytes() []byte {
+	bytes := make([]byte, 16)
+	binary.BigEndian.PutUint32(bytes[0:4], d.integer[3])
+	binary.BigEndian.PutUint32(bytes[4:8], d.integer[2])
+	binary.BigEndian.PutUint32(bytes[8:12], d.integer[1])
+	binary.BigEndian.PutUint32(bytes[12:16], d.integer[0])
+	var x big.Int
+	x.SetBytes(bytes)
+	if !d.positive {
+		x.Neg(&x)
+	}
+	return scaleBytes(x.String(), d.scale)
+}
+
+func scaleBytes(s string, scale uint8) []byte {
+	z := make([]byte, 0, len(s)+1)
+	if s[0] == '-' || s[0] == '+' {
+		z = append(z, byte(s[0]))
+		s = s[1:]
+	}
+	pos := len(s) - int(scale)
+	if pos <= 0 {
+		z = append(z, byte('0'))
+	} else if pos > 0 {
+		z = append(z, []byte(s[:pos])...)
+	}
+	if scale > 0 {
+		z = append(z, byte('.'))
+		for pos < 0 {
+			z = append(z, byte('0'))
+			pos++
+		}
+		z = append(z, []byte(s[pos:])...)
+	}
+	return z
+}
+
+func (d Decimal) String() string {
+	return string(d.Bytes())
+}