#103 Improve error message for event handler mismatch

[Vidar Hasfjord]

In OWLNext 6.40, with the introduction of the new implementation of Windows message dispatch, the error message given by the Microsoft and Clang-based Embarcadero compilers on an event handler signature mismatch got noticably worse. The error messages for these compilers are now non-specific and does not tell the user the correct signature, and may not even indicate the particular table entry at fault, instead pointing to the table as a whole. In particular, this makes migration from earlier versions difficult, since many event handler signatures changed in 6.40.

Proposed solution: Reintroduce explicit signature checks that provide better error messages on signature mismatch. This solution has already been implemented for Owlet [r3545].

See also: [news:2017/01/more-helpful-error-messages-for-event-handler-signature-mismatch].

[Vidar Hasfjord]

This request was implemented on the trunk in [r3630], based on the changes in Owlet [r3545], and the implementation was merged into 6.44 in [r3633].