Dict and Array constructor inconsistencies

[ingmarschuster]

Both Dict and Array are parametric types. Constructing a Dict and an Array of variable size differs markedly, though:
* Dict{TypeA,TypeB}()
* Array(Type) [while Array{Type}() doesnt work]
This creates some confusion for people new to the language - also I think its inconsitent design.

[pao]

Double posted; see #3214.