This fixes an issue when creating tracks or busses with a colon
in the name. Renaming those tracks later IO::set_name()
crashed in current_name.replace(std::string::npos,..).
`IO::build_legal_port_name` uses ";" instead of ":" while
`IO::set_name` replaced it with a "-".
Initially the IO name included the colon, so ports created
use a semicolon. But after renaming the IO, ::set_name() applies
the replacement and the IO's name is changed to include the "-".
This leads to a conflict with ports that already have the semicolon
in the port-name.
62aae6cffb