[PATCH v2] Detect if kdiff3 supports '--' and do not supply it if not supported

[Patrick Higgins <patrick.higgins@cexp.com>]

kdiff3 can be compiled with Qt only or with KDE support. If compiled with
Qt only, it does not support '--' and mergetool fails silently.

Signed-off-by: Patrick Higgins <patrick.higgins@cexp.com>
---
 git-mergetool.sh |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/git-mergetool.sh b/git-mergetool.sh
index fcdec4a..85ce004 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -181,12 +181,19 @@ merge_file () {
 
     case "$merge_tool" in
 	kdiff3)
+	    "$merge_tool_path" --auto -o /dev/null -- /dev/null /dev/null
+	    if test $? -ne 0; then
+		double_dash=""
+	    else
+		double_dash="--"
+	    fi
+
 	    if base_present ; then
 		("$merge_tool_path" --auto --L1 "$MERGED (Base)" --L2 "$MERGED (Local)" --L3 "$MERGED (Remote)" \
-		    -o "$MERGED" -- "$BASE" "$LOCAL" "$REMOTE" > /dev/null 2>&1)
+		    -o "$MERGED" $double_dash "$BASE" "$LOCAL" "$REMOTE" > /dev/null 2>&1)
 	    else
 		("$merge_tool_path" --auto --L1 "$MERGED (Local)" --L2 "$MERGED (Remote)" \
-		    -o "$MERGED" -- "$LOCAL" "$REMOTE" > /dev/null 2>&1)
+		    -o "$MERGED" $double_dash "$LOCAL" "$REMOTE" > /dev/null 2>&1)
 	    fi
 	    status=$?
 	    ;;
-- 
1.5.6.rc2