py3: use bytes.startswith() instead of comparing with bytes[0]
This is because bytes[0] will return the ascii value and comparison will fail.
This makes test-commit-interactive-curses.t pass on Python 3.
Differential Revision: https://phab.mercurial-scm.org/D5879
{
// 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)
}