Merge the 0.74 release branch back to master.

Two minor memory-leak fixes on 0.74 seem not to be needed on master:
the fix in an early exit path of pageant_add_keyfile is done already
on master in a different way, and the missing sfree(fdlist) in
uxsftp.c is in code that's been completely rewritten in the uxcliloop
refactoring.

Other minor conflicts: the rework in commit b52641644905 of
ssh1login.c collided with the change from FLAG_VERBOSE to
seat_verbose(), and master and 0.74 each added an unrelated extra
field to the end of struct SshServerConfig.

windows/window.c

@@ -5225,7 +5225,7 @@ static void wintw_clip_write(
                                    (int)udata[uindex]);
                     alen = 1; strcpy(after, "}");
                 } else {
-                    blen = sprintf(before, "\\u%d", udata[uindex]);
+                    blen = sprintf(before, "\\u%d", (int)udata[uindex]);
                     alen = 0; after[0] = '\0';
                 }
             }