#1013 assert in vhdlpp regarding type of concatentation

[Larry Doolittle]

Attached vhdl file triggers the assert in
const VTypeExpConcat::probe_type(Entity, ScopeBase*) const
where the comment says
"I don't know how to probe the type of a concatenation, quite yet."

$ iverilog -g2005-sv bug6.vhd
bug6.vhd:20: assert: .../vhdlpp/expression_elaborate.cc:757: failed assertion 0
Aborted
No top level modules, and no -s option.

This is as of Icarus (devel) (s20150603-437-ge56e52b).
The simplified test case is derived from a production UART module on ohwr.org, that also triggers the assert.