Remove the build number from emacs-version variable

It's a largely internal detail that can confuse users.  (Bug#25590)
* lisp/version.el (emacs-build-number): New constant.
(emacs-version): Use emacs-build-number.
* lisp/loadup.el (top-level): When dumping, increment
emacs-build-number rather than emacs-version.
* src/emacs.c (emacs-version): Doc fix.
* doc/lispref/intro.texi (Version Info): Update emacs-version details.
Mention emacs-build-number.
* lisp/gnus/gnus-util.el (gnus-emacs-version):
* lisp/mail/emacsbug.el (report-emacs-bug):
* admin/admin.el (set-version): Update for emacs-version change.
; * etc/NEWS: Mention this.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/emacs.c b/src/emacs.c
index 3083d0df302..e5305e27417 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -2607,7 +2607,12 @@ This is nil during initialization.  */);
   Vemacs_copyright = build_string (emacs_copyright);
 
   DEFVAR_LISP ("emacs-version", Vemacs_version,
-               doc: /* Version numbers of this version of Emacs.  */);
+               doc: /* Version numbers of this version of Emacs.
+This has the form: MAJOR.MINOR[.MICRO], where MAJOR/MINOR/MICRO are integers.
+MICRO is only present in unreleased development versions,
+and is not especially meaningful.  Prior to Emacs 26.1, an extra final
+component .BUILD is present.  This is now stored separately in
+`emacs-build-number'.  */);
   Vemacs_version = build_string (emacs_version);
 
   DEFVAR_LISP ("report-emacs-bug-address", Vreport_emacs_bug_address,