References of the form $var and ${var} both map to the same structure in
the AST, which prevents any later analysis functions from distinguishing
them. In preparation for adding checks that need this info, add a Bool
to T_DollarBraced that tracks whether the braces were seen at parsing
time and update all references so that this change is a no-op.
This is motivated by the fact that the popularity of bats is increasing
since the creation of bats-core/bats-core.
The code is a cherry-pick of koalaman/shellcheck/bats branch.
Fixkoalaman/shellcheck#417.
Vidar Holen
Benjamin Gordon
Virgil
Ng Zhi An
Oleg Grenrus