invalid subtyping (v0.6-dev.2481)

[JeffreySarnoff]

julia> Pkg.checkout("ASTInterpreter")
INFO: Checking out ASTInterpreter master...
INFO: Pulling ASTInterpreter latest master...
INFO: No packages to install, update or remove

julia> using ASTInterpreter
INFO: Precompiling module ASTInterpreter.
ERROR: LoadError: invalid subtyping in definition of PostOrderDFS
Stacktrace:
 [1] include_from_node1(::String) at ./loading.jl:539
 [2] include(::String) at ./sysimg.jl:14
 [3] anonymous at ./<missing>:2
while loading /home/jas/.julia/v0.6/AbstractTrees/src/AbstractTrees.jl, in expression starting on line 508
ERROR: LoadError: Failed to precompile AbstractTrees to /home/jas/.julia/lib/v0.6/AbstractTrees.ji.