bal/bs/bse/cf/is: show short monthnames in monthly reports (like html)

hledger/Hledger/Cli/Commands/Balance.hs

@@ -724,7 +724,7 @@ balanceReportAsTable opts (MultiBalanceReport (colspans, items, (coltotals,tot,a
      (map rowvals items)
   where
     mkDate = case balancetype_ opts of
-       PeriodChange -> showDateSpan
+       PeriodChange -> showDateSpanMonthAbbrev
        _            -> maybe "" (showDate . prevday) . spanEnd
     colheadings = map mkDate colspans
                   ++ (if row_total_ opts then ["  Total"] else [])

hledger/Hledger/Cli/CompoundBalanceCommand.hs

@@ -294,7 +294,7 @@ compoundBalanceReportAsCsv ropts (title, colspans, subreports, (coltotals, grand
   addtotals $
   padRow title :
   ("Account" :
-   map showDateSpan colspans
+   map showDateSpanMonthAbbrev colspans
    ++ (if row_total_ ropts then ["Total"] else [])
    ++ (if average_ ropts then ["Average"] else [])
    ) :