Allow <> as operator for property regexp matches.

When <> is used as the operator, the comparison test it true if the
regexp does *not* match the value of the property.

ORGWEBPAGE/Changes.org

@@ -27,8 +27,8 @@
     There are new values for the =:scope= parameter of a clock
     table.  This can now be =file-with-archives= and
     =agenda-with-archives=, in order to collect information not
-    only from the file org agenda files, but also all archive
-    files that are currently used by these files.
+    only from the current file or all agenda files, but also from
+    all archive files that are currently used by these files.
 
 *** New operators for property searches
 
@@ -44,12 +44,11 @@
     the operator, a string comparison is done: =+PRIORITY<"C".=
 
     Finally, if the right hand side is enclosed in curly braces,
-    a regexp match is done: =aaa={regexp}=.  You should use only
-    the `=' operator in this case.
+    a regexp match is done: =aaa={regexp}=.  In this case you
+    should use only the `=' or `<>' operators, meaning "does
+    match" or "does not match", respectively.
 
-    This was a simple change and should have been implemented a
-    long time ago - now it was finally triggered by a request
-    from Dan Davison.
+    This was a triggered with a request by Dan Davison.
 
 *** Orgtbl radio tables generalized.
 

doc/org.texi

@@ -3668,11 +3668,12 @@ and the allowed operators are @samp{<}, @samp{=}, @samp{>}, @samp{<=},
 @samp{>=}, and @samp{<>}.  If the comparison value is enclosed in double
 quotes, a string comparison is done, and the same operators are allowed.  If
 the comparison value is enclosed in curly braces, a regexp match is
-performed.  So the search string in the example finds entries tagged
-@samp{:work:} but not @samp{:boss:}, which also have a priority value
-@samp{A}, a @samp{:Coffee:} property with the value @samp{unlimited}, an
-@samp{Effort} property that is numerically smaller than 2, and a
-@samp{:With:} property that is matched by the regular expression
+performed, with @samp{=} meaning that the regexp matches the property value,
+and @samp{<>} meaning that it does not match.  So the search string in the
+example finds entries tagged @samp{:work:} but not @samp{:boss:}, which also
+have a priority value @samp{A}, a @samp{:Coffee:} property with the value
+@samp{unlimited}, an @samp{Effort} property that is numerically smaller than
+2, and a @samp{:With:} property that is matched by the regular expression
 @samp{Sarah\|Denny}.
 
 You can configure Org mode to use property inheritance during a search, but

lisp/org.el

@@ -8814,7 +8814,9 @@ also TODO lines."
 			 (setq gv '(get-text-property (point) 'org-category))
 		       (setq gv `(org-cached-entry-get nil ,pn)))
 		     (if re-p
-			 `(string-match ,pv (or ,gv ""))
+			 (if (eq po 'org<>)
+			     `(not (string-match ,pv (or ,gv "")))
+			   `(string-match ,pv (or ,gv "")))
 		       (if str-p
 			   `(,po (or ,gv "") ,pv)
 			 `(,po (string-to-number (or ,gv ""))