(ada-prj-default-check-cmd): New variable, replacing deleted variable
`ada-check-switch'.
(ada-project-file-extension): Rename to `ada-prj-file-extension'.
(ada-xref-project-files): Improve doc string.
(ada-find-executable): New function.
(ada-initialize-runtime-library): Use `ada-find-executable'.
(ada-xref-set-default-prj-values): In compile commands, don't
need `ada-cd-command'; `compile' does that more portably.
Use ada-prj-default-check-cmd.
(ada-parse-prj-file): Don't set 'debug_post_cmd, 'debug_pre_cmd
properties if not specified in project file.
(ada-goto-declaration): Display useful message for new error
'error-file-not-found.
(ada-get-ada-file-name, ada-find-in-src-path): Signal new error
'error-file-not-found.
(ada-get-all-references): Match latest ali syntax.
Signal new error 'error-file-not-found.
(ada-find-in-ali): Match latest ali syntax.
(ada-make-filename-from-adaname): Handle different semantics
of gnatkr in GNAT 3.15p vs later.