* lisp/subr.el (define-error): New function.

* lisp/subr.el (define-error): New function.
* doc/lispref/control.texi (Signaling Errors): Refer to define-error.
(Error Symbols): Add `define-error'.
* doc/lispref/errors.texi (Standard Errors): Don't refer to `error-conditions'.
* lisp/progmodes/ada-xref.el (ada-error-file-not-found): Rename from
error-file-not-found and define with define-error.
* lisp/emacs-lisp/cl-lib.el (cl-assertion-failed): Move here from subr.el
and define with define-error.
* lisp/userlock.el (file-locked, file-supersession):
* lisp/simple.el (mark-inactive):
* lisp/progmodes/js.el (js-moz-bad-rpc, js-js-error):
* lisp/progmodes/ada-mode.el (ada-mode-errors):
* lisp/play/life.el (life-extinct):
* lisp/nxml/xsd-regexp.el (xsdre-invalid-regexp, xsdre-parse-error):
* lisp/nxml/xmltok.el (xmltok-markup-declaration-parse-error):
* lisp/nxml/rng-util.el (rng-error):
* lisp/nxml/rng-uri.el (rng-uri-error):
* lisp/nxml/rng-match.el (rng-compile-error):
* lisp/nxml/rng-cmpct.el (rng-c-incorrect-schema):
* lisp/nxml/nxml-util.el (nxml-error, nxml-file-parse-error):
* lisp/nxml/nxml-rap.el (nxml-scan-error):
* lisp/nxml/nxml-outln.el (nxml-outline-error):
* lisp/net/soap-client.el (soap-error):
* lisp/net/gnutls.el (gnutls-error):
* lisp/net/ange-ftp.el (ftp-error):
* lisp/mpc.el (mpc-proc-error):
* lisp/json.el (json-error, json-readtable-error, json-unknown-keyword)
(json-number-format, json-string-escape, json-string-format)
(json-key-format, json-object-format):
* lisp/jka-compr.el (compression-error):
* lisp/international/quail.el (quail-error):
* lisp/international/kkc.el (kkc-error):
* lisp/emacs-lisp/ert.el (ert-test-failed):
* lisp/calc/calc.el (calc-error, inexact-result, math-overflow)
(math-underflow):
* lisp/bookmark.el (bookmark-error-no-filename):
* lisp/epg.el (epg-error): Define with define-error.