Tests fail if core and show run on same worker

[tkelman]

bisected to 1b470f5

$ JULIA_CPU_CORES=1 usr/bin/julia test/runtests.jl core show
     * core                 WARNING: Method definition f( in Tuple{Vararg{ Int6418, .#N<:12Any seconds, maxrss } }, 288AbstractArray.{29#T<:Any MB
,      * #N<:Anyshow})  in module Main  at C:\cygwin64\home\Tony\julia\test\core.jl:706 overwritten  at C:\cygwin64\home\Tony\julia\test\core.jl:712.
 WARNING: Method definition f ()  in module JLCall14301 at C:\cygwin64\home\Tony\julia\test\core.jl:3528  overwritten at C:\cygwin64\home\Tony\julia\test\core.jl:3538 .
         ERROR: LoadError: LoadError: MethodError: no method matching directsubtype(::TypeVar, ::Type{B11327})
Closest candidates are:
  directsubtype(!Matched::DataType, ::DataType)
  directsubtype(!Matched::TypeConstructor, ::DataType)
  directsubtype(!Matched::Union, ::DataType)
 in mapreduce_sc_impl(::Base.Predicate{Base.##235#236{DataType}}, ::Base.#|, ::SimpleVector) at .\reduce.jl:198
 in any(::Function, ::SimpleVector) at .\reduce.jl:378
 in directsubtype(::Union, ::DataType) at .\show.jl:1174
 in directsubtype(::TypeConstructor, ::DataType) at .\show.jl:1173
 in dumpsubtypes(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::DataType, ::Module, ::Int64, ::String) at .\show.jl:1184
 in dumptype(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Any, ::Int64, ::String) at .\show.jl:1168
 in dumpsubtypes(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::DataType, ::Module, ::Int64, ::String) at .\show.jl:1200
 in dumptype(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Any, ::Int64, ::String) at .\show.jl:1168
 in dumpsubtypes(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::DataType, ::Module, ::Int64, ::String) at .\show.jl:1200
 in dumptype(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::Any, ::Int64, ::String) at .\show.jl:1168
 in #dump#237(::Int64, ::Function, ::Base.AbstractIOBuffer{Array{UInt8,1}}, ::DataType) at .\show.jl:1211
 in dump(::Base.AbstractIOBuffer{Array{UInt8,1}}, ::DataType) at .\show.jl:1211
 in #sprint#221(::Void, ::Function, ::Int64, ::Function, ::Type{T}, ::Vararg{Type{T},N}) at .\strings\io.jl:35
 in sprint(::Function, ::Type{T}) at .\strings\io.jl:39
 in include_from_node1(::String) at .\loading.jl:426
 in macro expansion at .\util.jl:180 [inlined]
 in runtests(::String) at C:\cygwin64\home\Tony\julia\test\testdefs.jl:7

[yuyichao]

The issue seems to be the TypeVar in typealias Maybe7049{T} Union{T,Void}.