Log more/better messages when message fails to post (e.g. duplicate detected)

It appears I had the idea to make the CantPost text.dat string a format string
before, but never quite finished that change (e.g. made the change to
email.cpp and text.dat too).

ctrl/text.dat

@@ -915,7 +915,7 @@
 "\1n\r\nSorry, you can't edit this message.\r\n"	757 CantEditMsg
 "\1n\r\nSorry, you can't delete message #%u.\r\n"	758 CantDeleteMsg
 "\1n\r\nSorry, you can't read messages on %s %s\r\n"	759 CantReadSub
-"\1n\r\nSorry, you can't post that message.\r\n"	760 CantPostMsg
+"\rSorry, you can't post that message. Reason: %s\r\n"	760 CantPostMsg
 "\r\n\1y\1hOperator: \1w"				761 OperatorPrompt
 "Add this sub-board to your new-scan list"         762 AddSubToNewScanQ
 "\1n\1r\1iWARNING: You are reading messages past the last unvalidated message (%u)" 763 UnvalidatedWarning

src/sbbs3/email.cpp

@@ -258,8 +258,7 @@ bool sbbs_t::email(int usernumber, const char *top, const char *subj, int mode,
 			smb_unlocksmbhdr(&smb);
 			smb_close(&smb);
 			smb_stack(&smb,SMB_STACK_POP);
-			attr(cfg.color[clr_err]);
-			bputs(text[CantPostMsg]);
+			bprintf(text[CantPostMsg], i == SMB_DUPE_MSG ? "duplicate" : "other");
 			return(false); 
 		} 
 	}

src/sbbs3/postmsg.cpp

@@ -312,17 +312,21 @@ bool sbbs_t::postmsg(int subnum, int wm_mode, smb_t* resmb, smbmsg_t* remsg)
 	i=smb_addmsg(&smb,&msg,storage,dupechk_hashes,xlat,(uchar*)msgbuf, findsig(msgbuf));
 	free(msgbuf);
 
-	if(i==SMB_DUPE_MSG) {
-		attr(cfg.color[clr_err]);
-		bprintf(text[CantPostMsg], smb.last_error);
-	} else if(i!=SMB_SUCCESS)
+	if(i==SMB_DUPE_MSG)
+		bprintf(text[CantPostMsg], "duplicate");
+	else if(i!=SMB_SUCCESS)
 		errormsg(WHERE,ERR_WRITE,smb.file,i,smb.last_error);
 
 	smb_close(&smb);
 	smb_stack(&smb,SMB_STACK_POP);
 	smb_freemsgmem(&msg);
-	if(i!=SMB_SUCCESS)
-		return(false); 
+	if(i!=SMB_SUCCESS) {
+		if(i == SMB_DUPE_MSG)
+			llprintf(LOG_NOTICE, "P!", "duplicate message post attempt in %s", cfg.sub[subnum]->code);
+		else
+			llprintf(LOG_NOTICE, "P!", "message posting failure (SMB error %d) in %s", i, cfg.sub[subnum]->code);
+		return false;
+	}
 
 	logon_posts++;
 	user_posted_msg(&cfg, &useron, 1);