Fixed ICML image syntax for local files.

`file:filename` rather than `file://./filename`.

I think this is right; it matches what we had before
with people actually using the ICML writer, and seems
to match examples in the spec.  I don't
have a copy of InDesign I can test on, though.
@DigitalPublishingToolkit and @mb21, can you have
a look?

src/Text/Pandoc/Writers/ICML.hs

@@ -533,7 +533,7 @@ imageICML opts style attr _ (src, _) = do
       hw = showFl $ ow / 2
       hh = showFl $ oh / 2
       scale = showFl (imgWidth / ow) ++ " 0 0 " ++ showFl (imgHeight / oh)
-      src' = if isURI src then src else "file://." ++ pathSeparator : src
+      src' = if isURI src then src else "file:" ++ src
       (stlStr, attrs) = styleToStrAttr style
       props  = inTags True "Properties" [] $ inTags True "PathGeometry" []
                  $ inTags True "GeometryPathType" [("PathOpen","false")]

tests/writer.icml

@@ -2563,7 +2563,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{</Content>
             $ID/Embedded
           </Profile>
         </Properties>
-        <Link Self="ueb" LinkResourceURI="file://./lalune.jpg" />
+        <Link Self="ueb" LinkResourceURI="file:lalune.jpg" />
       </Image>
     </Rectangle>
   </CharacterStyleRange><Br />
@@ -2592,7 +2592,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{</Content>
             $ID/Embedded
           </Profile>
         </Properties>
-        <Link Self="ueb" LinkResourceURI="file://./movie.jpg" />
+        <Link Self="ueb" LinkResourceURI="file:movie.jpg" />
       </Image>
     </Rectangle>
   </CharacterStyleRange>