dpkg: Reverse --verify-format logic to accept 'rpm' as valid

Closes: #765907

debian/changelog

@@ -11,6 +11,8 @@ dpkg (1.17.19) UNRELEASED; urgency=low
   * Mention --pid and --ppid in start-stop-daemon(8) man page DESCRIPTION.
   * Add invoke hooks for dpkg --add-architecture and --remove-architecture.
     Prompted by Helmut Grohne <helmut@subdivi.de>.
+  * Reverse --verify-format logic to actually accept 'rpm' as valid.
+    Closes: #765907
 
   [ Updated programs translations ]
   * Italian (Milo Casagrande): Closes: #765748

src/main.h

@@ -178,7 +178,7 @@ int cmpversions(const char *const *argv);
 
 /* from verify.c */
 
-int verify_set_output(const char *name);
+bool verify_set_output(const char *name);
 int verify(const char *const *argv);
 
 /* from select.c */

src/verify.c

@@ -81,15 +81,15 @@ verify_output_rpm(struct filenamenode *namenode, struct verify_checks *checks)
 
 static verify_output_func *verify_output = verify_output_rpm;
 
-int
+bool
 verify_set_output(const char *name)
 {
 	if (strcmp(name, "rpm") == 0)
 		verify_output = verify_output_rpm;
 	else
-		return 1;
+		return false;
 
-	return 0;
+	return true;
 }
 
 static void