ConTeXt writer: Properly handle tables without captions.

The old output only worked in MkII. This should work in MkIV
as well.

Closes #837.

src/Text/Pandoc/Writers/ConTeXt.hs

@@ -203,9 +203,11 @@ blockToConTeXt (Table caption aligns widths heads rows) = do
                   then return empty
                   else liftM ($$ "\\HL") $ tableRowToConTeXt heads
     captionText <- inlineListToConTeXt caption
-    let captionText' = if null caption then text "none" else captionText
     rows' <- mapM tableRowToConTeXt rows
-    return $ "\\placetable[here]" <> braces captionText' $$
+    return $ "\\placetable" <> brackets ("here" <> if null caption
+                                                      then ",none"
+                                                      else "")
+                            <> braces captionText $$
              "\\starttable" <> brackets (text colDescriptors) $$
              "\\HL" $$ headers $$
              vcat rows' $$ "\\HL" $$ "\\stoptable" <> blankline

tests/tables.context

@@ -29,7 +29,7 @@ Simple table with caption:
 
 Simple table without caption:
 
-\placetable[here]{none}
+\placetable[here,none]{}
 \starttable[|r|l|c|l|]
 \HL
 \NC Right
@@ -111,7 +111,7 @@ Multiline table with caption:
 
 Multiline table without caption:
 
-\placetable[here]{none}
+\placetable[here,none]{}
 \starttable[|cp(0.15\textwidth)|lp(0.14\textwidth)|rp(0.16\textwidth)|lp(0.34\textwidth)|]
 \HL
 \NC Centered Header
@@ -135,7 +135,7 @@ Multiline table without caption:
 
 Table without column headers:
 
-\placetable[here]{none}
+\placetable[here,none]{}
 \starttable[|r|l|c|r|]
 \HL
 \NC 12
@@ -158,7 +158,7 @@ Table without column headers:
 
 Multiline table without column headers:
 
-\placetable[here]{none}
+\placetable[here,none]{}
 \starttable[|cp(0.15\textwidth)|lp(0.14\textwidth)|rp(0.16\textwidth)|lp(0.34\textwidth)|]
 \HL
 \NC First