bug#64198: Feature request: compile.el's "Find this in" prompt should be hookable.

[Dave Abrahams]

[I hope this is the right venue for feature requests.  If not, sorry!]

When a file can't be found via the path given in a diagnostic, I'd like to be 
able to override the prompt that emacs gives to locate the file.  
compilation-parse-errors-filename-function happens too early, while the buffer 
is being initially parsed.  A similar compilation-locate-file-function would be 
great.  If there's interest I could try to develop a patch.