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.

import.c

@@ -572,8 +572,10 @@ static ssh2_userkey *openssh_pem_read(
     strbuf *blob = strbuf_new_nm();
     int privptr = 0, publen;
 
-    if (!key)
+    if (!key) {
+        strbuf_free(blob);
         return NULL;
+    }
 
     if (key->encrypted) {
         unsigned char keybuf[32];