The new version of the daemon has the "alt_chain_info" command. The output looks like:
5 alternate chains found:
1 blocks long, from height 1264997 (5502 deep), diff 1746032035727893: 57519747c6f430928b39aaab4f68515640b219401ed3f8ce147ceadb1ce21e73
1 blocks long, from height 1269997 (502 deep), diff 1783031745233488: 4137fc903c86833cc876bc909a4286222e3eddb86a2f425d50180b2aa80858bc
1 blocks long, from height 1261802 (8697 deep), diff 1724749748888991: d2c43ed9754d9ffbbe22841b72dc7999d0521bcc0c63b62de38155315db3618c
1 blocks long, from height 1267367 (3132 deep), diff 1764072489331929: c209106962ffcf53d20502d19ef8bf4c5945d6b9f2d2af45c9f345ffc3d3f9ed
1 blocks long, from height 1270427 (72 deep), diff 1785919159112029: d5f4e42683b41ea68d2f1c7e1319cdca8df162dab7295d9d00e14230856a3c63
How does one interpret the output and how do I know that I'm on the "official" chain and not on an alternative one?