If 金鸡独立 is limited to the edge of the board, then 金鸡独立 is distinct from a double shortage of liberties. A double shortage of liberties could occur far from any edge. Would a double shortage of liberties be called 双气紧 and the term 金鸡独立 used only for a double shortage of liberties created by a descent to the edge of the board ?
I did a google search for 金鸡独立, and found the following page as one of the first hits.
This link is definitely NOT safe for work!
http://www.ljdy.ca/html/2007-07/2682.htm
"Standing on one leg", indeed! :-0