Use inference in dot completion FIX #10091.

[dhoegh]

This adds inference in to dot completion. Examples of this use

julia> split("","")[1].<tab>
endof  offset  string
julia> IOBuffer().<tab>
append   data      mark      maxsize   ptr       readable  seekable  size      writable

More elaborate examples can be seen in the test/replcompletions.jl.

cc @blakejohnson could you review this as you reviewed similar changes in #11679.
note: This uses the same framework for dot completion as I added in #11679 for method completion. The second commit improves get_type_call logic, so it is more general and hence can figure the return types from more elaborate expressions.

[dhoegh]

The Travis failure seems unrelated.

[dhoegh]

Bump, any comments on the code or the feature it introduces?