Underscore replacement should recurse into quasiquote

[c42f]

Expr(:quote) is actually a quasiquote, so the following should be equivalent:

julia> map(i->:(a[$i]), 1:4)
4-element Array{Expr,1}:
 :(a[1])
 :(a[2])
 :(a[3])
 :(a[4])

julia> @_ map(:(a[$_]), 1:4)
ERROR: syntax: all-underscore identifier used as rvalue
Stacktrace:
 [1] top-level scope at REPL[2]:1