Add Array#reject_bang
Merge pull request #2098 from suzukaze/add-array.reject_bang

 Add Array#reject!
adjust indent
fix optional block arguments in rhs

define optional block arguments as argument variables in the rhs
default expressions, as same as mere assignment expressions.

Import ruby/ruby@01740f0c273c89f7bcff3d5014d73c8ff6fb1986
Merge pull request #2099 from nobu/optional_arguments_in_rhs

Optional arguments in rhs