Fix actor fontification error

Lines would get incorrectly fontified when line contained more than one
colon.

This closes #37

test-files/fontification-double-colon.wsd

@@ -0,0 +1,7 @@
+
+title Double colon fontification error (as outligned in github issue 37)
+
+pc->pc: This line highlight's actor just fine
+pc->pc: This line doesn't, because of a double : sign.
+pc->pc: But next line is just fine again.
+

wsd-mode.el

@@ -260,10 +260,10 @@
                                                          (wsd-rx-word "as")
                                                          "\\(.+\\)$")))
 
-                 ;; actors in activity staements
+                 ;; actors in activity statements
                  (rx-actors (wsd-rx-lstart (concat "\\([^\n-]+\\)"
                                                    (regexp-opt wsd-operators3 t)
-                                                   "\\(.+\\)"
+                                                   "\\([^:]+\\)"
                                                    ":.*$")))
 
                  ;; actors in activate/deactivate/destroy statements

wsd-tests.el

@@ -160,6 +160,19 @@
                  'font-lock-variable-name-face
                  (face-at-point)))))))
 
+(ert-deftest statement-actors-are-fontified-as-variables ()
+  (let* ((buffer (find-file-read-only "test-files/fontification-double-colon.wsd")))
+    ;; double-ensure mode is active
+    (wsd-mode)
+    ;; required when running in unit-test runner.
+    (font-lock-fontify-buffer)
+
+    (while (search-forward "pc" nil t)
+      (backward-char 1)
+      (should (eql
+               'font-lock-variable-name-face
+               (face-at-point))))))
+
 (ert-deftest indentation-reference-document-is-reflowed-correctly ()
   (let* ((buffer (find-file "test-files/indentation-tests.wsd")))
     ;; double ensure mode is active