First cut at displaying the diffs for a merge.

We display the files where the child differs from the first parent
first in black in the file list window, followed by the second parent
in blue, and so on using different colors for each parent (provided
you don't have more than 6 parents; if you do we cycle around).

gitk

@@ -1684,13 +1684,25 @@ proc selectline {l} {
 
     $cflist delete 0 end
     $cflist insert end "Comments"
-    if {$nparents($id) == 1} {
+    startdiff $id $parents($id)
-	startdiff [concat $id $parents($id)]
-    }
-    catch {unset seenfile}
 }
 
-proc startdiff {ids} {
+proc startdiff {id vs} {
+    global diffpending diffpindex
+    global diffindex difffilestart seenfile
+    global curdifftag curtagstart
+
+    set diffpending $vs
+    set diffpindex 0
+    catch {unset seenfile}
+    set diffindex 0
+    catch {unset difffilestart}
+    set curdifftag Comments
+    set curtagstart 0.0
+    contdiff [list $id [lindex $vs 0]]
+}
+
+proc contdiff {ids} {
     global treediffs diffids treepending
 
     if {![info exists treediffs($ids)]} {
@@ -1712,9 +1724,13 @@ proc selnextline {dir} {
 }
 
 proc addtocflist {ids} {
-    global treediffs cflist
+    global treediffs cflist diffpindex
+
+    set colors {black blue green red cyan magenta}
+    set color [lindex $colors [expr {$diffpindex % [llength $colors]}]]
     foreach f $treediffs($ids) {
 	$cflist insert end $f
+	$cflist itemconf end -foreground $color
     }
     getblobdiffs $ids
 }
@@ -1741,7 +1757,6 @@ proc gettreediffline {gdtf ids} {
 	    if {$ids != $diffids} {
 		gettreediffs $diffids
 	    } else {
-		unset diffids
 		addtocflist $ids
 	    }
 	}
@@ -1752,8 +1767,8 @@ proc gettreediffline {gdtf ids} {
 }
 
 proc getblobdiffs {ids} {
-    global diffopts blobdifffd blobdiffids env curdifftag curtagstart
+    global diffopts blobdifffd diffids env
-    global diffindex difffilestart nextupdate
+    global nextupdate
 
     set id [lindex $ids 0]
     set p [lindex $ids 1]
@@ -1763,33 +1778,33 @@ proc getblobdiffs {ids} {
 	return
     }
     fconfigure $bdf -blocking 0
-    set blobdiffids $ids
     set blobdifffd($ids) $bdf
-    set curdifftag Comments
+    fileevent $bdf readable [list getblobdiffline $bdf $ids]
-    set curtagstart 0.0
-    set diffindex 0
-    catch {unset difffilestart}
-    fileevent $bdf readable "getblobdiffline $bdf {$ids}"
     set nextupdate [expr {[clock clicks -milliseconds] + 100}]
 }
 
 proc getblobdiffline {bdf ids} {
-    global blobdiffids blobdifffd ctext curdifftag curtagstart seenfile
+    global diffids blobdifffd ctext curdifftag curtagstart seenfile
     global diffnexthead diffnextnote diffindex difffilestart
-    global nextupdate
+    global nextupdate diffpending diffpindex
 
     set n [gets $bdf line]
     if {$n < 0} {
 	if {[eof $bdf]} {
 	    close $bdf
-	    if {$ids == $blobdiffids && $bdf == $blobdifffd($ids)} {
+	    if {$ids == $diffids && $bdf == $blobdifffd($ids)} {
 		$ctext tag add $curdifftag $curtagstart end
 		set seenfile($curdifftag) 1
+		if {[incr diffpindex] < [llength $diffpending]} {
+		    set id [lindex $ids 0]
+		    set p [lindex $diffpending $diffpindex]
+		    contdiff [list $id $p]
+		}
 	    }
 	}
 	return
     }
-    if {$ids != $blobdiffids || $bdf != $blobdifffd($ids)} {
+    if {$ids != $diffids || $bdf != $blobdifffd($ids)} {
 	return
     }
     $ctext conf -state normal
@@ -1882,7 +1897,7 @@ proc nextfile {} {
 }
 
 proc listboxsel {} {
-    global ctext cflist currentid treediffs seenfile
+    global ctext cflist currentid treediffs
     if {![info exists currentid]} return
     set sel [lsort [$cflist curselection]]
     if {$sel eq {}} return