Minor cleanup for compile.el and grep.el.

Minor cleanup for compile.el and grep.el.
* lisp/progmodes/compile.el: Cleanup text-properties namespace by using
`compilation-message' instead of `message', `compilation-directory'
instead of `directory', and `compilation-debug' instead of `debug'.
(compilation-last-buffer, compilation-parsing-end)
(compilation-error-list, compilation-old-error-list): Move to the
compatibility part of the code.
(compilation-error-properties): If `file' is a function, let it return
a file name.
(compilation-mode-font-lock-keywords): Be more conservative with the
omake "^ *" pattern prefix, to try and minimize the risk of
pathologically slow regexp matching.
(compilation-start): Use inhibit-read-only.
(compilation--unsetup): New function.
(compilation-shell-minor-mode, compilation-minor-mode): Use it.
(compilation-filter): Minor tweaks.
(compilation-next-error-function): Try and avoid abusing variable names.
(compilation--flush-file-structure): New fun.
(compilation-fake-loc): Use it for cleaner behavior when file is reused.
(debug-ignored-errors): Add "Moved past last ...".
(compilation--compat-error-properties)
(compilation--compat-parse-errors): Rename by doubling the "-".

* lisp/progmodes/grep.el (grep-regexp-alist): Tighten regexp.
(grep-mode-font-lock-keywords): Remove regexp that seems like
a left-over from before we used compile.el.
(grep-mode-font-lock-keywords): Call syntax-ppss-flush-cache when
modifying the buffer within with-silent-modifications.