add HAE add-on

(cherry picked from commit d82486cfc3d08daf225d3aba206d44b8e553160b)
Do not hardcode path that we have in a variable

(cherry picked from commit dd2c24a4d813252026e4398c6d49205a2572118c)
Only consider HAE repos if available

(cherry picked from commit 302d896177b80bbc511ed93c196701bdccb4c63b)
Add some comments

(cherry picked from commit 49b4fd0decf56446c5ffa768c6537b7ae36d09a1)
Merge pull request #279 from vuntz/hae-stoney

Sync with roxy