@-commands in @errormsg

[Gavin Smith]

Hello everyone, I intend to remove the feature where @-commands can be
used in the argument to @errormsg. The reason for this is that I am
trying to rewrite the Texinfo::Parser module in C, and this feature is
implemented by the Texinfo::Parser module relying on
Texinfo::Convert::Text. It would be a significant complication to get
this to work in the C implementation. I don't think it's a very
important feature - it does provide some benefits, like being able to
use accent commands in error messages - but I don't think it's worth
it at this stage. I doubt that this feature is used that much anyway.
It may be possible to reinstate this feature at a later stage.