Add new status-fd action when disappearing a package

This will help front-ends like APT to keep better track of the actions
done during a dpkg run.

Closes: #537338

debian/changelog

@@ -38,6 +38,7 @@ dpkg (1.15.5) UNRELEASED; urgency=low
     Thanks to Robert Millan.
   * Update the FSF postal address in the source code license headers by
     replacing it with a URL to the gnu.org page.
+  * Add a new status-fd action when disappearing a package. Closes: #537338
 
   [ Raphaël Hertzog ]
   * Add versioned dependency on base-files (>= 5.0.0) to dpkg-dev to ensure

man/dpkg.1

@@ -542,7 +542,7 @@ User is being asked a conffile question.
 .BI "processing: " stage ": " package
 Sent just before a processing stage starts. \fIstage\fR is one of
 .BR upgrade ", " install " (both sent before unpacking),"
-.BR configure ", " trigproc  ", " remove  ", " purge .
+.BR configure ", " trigproc  ", " disappear ", " remove  ", " purge .
 .RE
 .TP
 \fB\-\-log=\fP\fIfilename\fP

src/processarc.c

@@ -1040,6 +1040,7 @@ void process_archive(const char *filename) {
 
     printf(_("(Noting disappearance of %s, which has been completely replaced.)\n"),
            otherpkg->name);
+    log_action("disappear", otherpkg->name);
     debug(dbg_general, "process_archive disappearing %s",otherpkg->name);
     /* No, we're disappearing it.  This is the wrong time to go and
      * run maintainer scripts and things, as we can't back out.  But