Julia v0.6 depwarn, ambiguity, and other misc fixes

• Fix an ambiguities in SortedDict, SortedMultiDict constructors
• Fix 0.6 typealias depwarn
• Fix 0.6 abstract type declaration depwarn
• Fix 0.6 misc other depwarns
• Fix push!(x::Accumulator,...) ambiguous function definitions
• Fix typing in BinaryHeap type
• Remove eval from DefaultDict constructor

Fix deprecation warnings on Julia 0.6

Julia 0.6 fixes (#257)

* Julia 0.6 fixes
* Remove recently introduced TypeVars.
* Don't allow failure on nightly

unbreak gadfly

Merge pull request #247 from tkelman/pinned.4a9edb3a.tmp

Revert "Remove HashDict"

v0.5.0: Merge pull request #238 from ararslan/aa/priorityqueue

Move PriorityQueue over from Base

v0.4.3: Merge pull request #181 from JuliaLang/guy_changelog

update changelog for 0.4.3