Markdown/RST writers: Only autolink absolute URIs.

This fixes a regression and closes #830.

    $ echo '<a href="x">x</a>' | pandoc -f html -t markdown
    <x>

src/Text/Pandoc/Writers/Markdown.hs

@@ -44,6 +44,7 @@ import qualified Data.Set as Set
 import Text.Pandoc.Writers.HTML (writeHtmlString)
 import Text.Pandoc.Readers.TeXMath (readTeXMath)
 import Text.HTML.TagSoup (renderTags, parseTags, isTagText, Tag(..))
+import Network.URI (isAbsoluteURI)
 import Data.Default
 
 type Notes = [[Block]]
@@ -680,7 +681,8 @@ inlineToMarkdown opts (Link txt (src, tit)) = do
                      then empty
                      else text $ " \"" ++ tit ++ "\""
   let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
-  let useAuto = case txt of
+  let useAuto = isAbsoluteURI src &&
+                case txt of
                       [Str s] | escapeURI s == srcSuffix -> True
                       _                                  -> False
   let useRefLinks = writerReferenceLinks opts && not useAuto

src/Text/Pandoc/Writers/RST.hs

@@ -36,6 +36,7 @@ import Text.Pandoc.Options
 import Text.Pandoc.Shared
 import Text.Pandoc.Templates (renderTemplate)
 import Data.List ( isPrefixOf, intersperse, transpose )
+import Network.URI (isAbsoluteURI)
 import Text.Pandoc.Pretty
 import Control.Monad.State
 import Control.Applicative ( (<$>) )
@@ -364,9 +365,10 @@ inlineToRST (LineBreak) = return cr -- there's no line break in RST (see Para)
 inlineToRST Space = return space
 -- autolink
 inlineToRST (Link [Str str] (src, _))
-  | if "mailto:" `isPrefixOf` src
-    then src == escapeURI ("mailto:" ++ str)
-    else src == escapeURI str = do
+  | isAbsoluteURI src &&
+    if "mailto:" `isPrefixOf` src
+       then src == escapeURI ("mailto:" ++ str)
+       else src == escapeURI str = do
   let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
   return $ text srcSuffix
 inlineToRST (Link [Image alt (imgsrc,imgtit)] (src, _tit)) = do