ui, web: show fewer other accounts in acct register

To reduce noise in the "other accounts" field of hledger-ui's and
hledger-web's account register: if there are both real and virtual
postings to other accounts, show only the accounts posted to by real
postings.

Use case: in many transactions I have extra balanced-virtual postings
which adjust budget envelopes (subaccounts of checking). These clutter
up the register's other accounts field making it useless. Excluding them
(when there are also real postings) makes it more useful for me and
probably others.

hledger-lib/Hledger/Reports/TransactionsReports.hs

@@ -201,8 +201,14 @@ accountTransactionsReportItems query thisacctquery bal signfn (torig:ts) =
 --       (froms,tos) = partition (fromMaybe False . isNegativeMixedAmount . pamount) ps
 
 -- | Generate a simplified summary of some postings' accounts.
+-- To reduce noise, if there are both real and virtual postings, show only the real ones.
 summarisePostingAccounts :: [Posting] -> String
-summarisePostingAccounts = intercalate ", " . map accountSummarisedName . nub . map paccount
+summarisePostingAccounts ps =
+  (intercalate ", " . map accountSummarisedName . nub . map paccount) displayps
+  where
+    realps = filter isReal ps
+    displayps | null realps = ps
+              | otherwise   = realps
 
 filterTransactionPostings :: Query -> Transaction -> Transaction
 filterTransactionPostings m t@Transaction{tpostings=ps} = t{tpostings=filter (m `matchesPosting`) ps}