Write header immediately in AbortWithStatus()

Otherwise, caller needs to invoke WriteHeaderNow himself after
AbortWithStatus(), which is error-prone.

Also modified ErrorLoggerT() such that it always writes log to response
body. Otherwise calling AbortWithStatus() will fail to write body because
c.Writer.Written() is set true by WriteHeaderNow().

context.go

@@ -115,6 +115,7 @@ func (c *Context) Abort() {
 // For example, a failed attempt to authentificate a request could use: context.AbortWithStatus(401).
 func (c *Context) AbortWithStatus(code int) {
 	c.Status(code)
+	c.Writer.WriteHeaderNow()
 	c.Abort()
 }