Add warning about using inline pgp with format=flowed. (closes #3963)

The reporter noted that when trying to use inline signing with
format=flowed, the flowed was turned off.

After some research, this appears to be deliberate, probably because
of strange interactions between inline PGP and format=flowed.  In fact
the RFC strongly discourages their combined use:
https://tools.ietf.org/html/rfc3676#section-4.6

Add a warning and prompt to use PGP/MIME in mutt_protect().

1 files changed, 10 insertions, 0 deletions

diff --git a/crypt.c b/crypt.c
index 5804c148..19a585d0 100644
--- a/crypt.c
+++ b/crypt.c
@@ -153,6 +153,16 @@ int mutt_protect (HEADER *msg, char *keylist)
         return -1;
       }
     }
+    else if (!mutt_strcasecmp ("flowed",
+                               mutt_get_parameter ("format", msg->content->parameter)))
+    {
+      if ((i = query_quadoption (OPT_PGPMIMEAUTO,
+              _("Inline PGP can't be used with format=flowed.  Revert to PGP/MIME?"))) != MUTT_YES)
+      {
+        mutt_error _("Mail not sent: inline PGP can't be used with format=flowed.");
+        return -1;
+      }
+    }
     else
     {
       /* they really want to send it inline... go for it */