I was having the same problem. Just worked when I installed using git. Try these steps:
1 - Install git
https://git-scm.com/downloads2 - Install Arduino 1.6.8
3 - Go to Arduino directory
4 - Clone this repository into hardware/esp8266com/esp8266 directory (or clone it elsewhere and create a symlink)
5 - Open the command prompt as adm
6 - use theses command lines:
cd hardware
mkdir esp8266com
cd esp8266com
git clone
https://github.com/esp8266/Arduino.git esp8266
7 - Download binary tools (you need Python 2.7)
cd esp8266/tools
python get.py
8 - Restart Arduino
It worked for me. The source of this is at
https://github.com/esp8266/arduino