revset: move subscript relation functions to its own dict
This will help adding more relation functions in extensions.
We skip short names (that consist of one letter) while raising
UnknownIdentifier because such names cannot be suggested anyway: the similarity
cutoff in dispatch._getsimilar() is currently 0.6.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}