changeset_printer: change flush() to accept ctx instead of rev

changeset_printer: change flush() to accept ctx instead of rev

Because flush() is the function to write data buffered by show(ctx),
flush(ctx) is more consistent than flush(rev). This makes sure that
buffered header and hunk are always keyed by ctx.rev().

This patch will allow us to give an integer to the wdir while keeping
wctx.rev() -> None.

--- a/mercurial/cmdutil.py	Sat Jul 04 17:19:49 2015 +0900
+++ b/mercurial/cmdutil.py	Sun Apr 12 21:52:02 2015 +0900
@@ -1119,7 +1119,8 @@
         self.lastheader = None
         self.footer = None
 
-    def flush(self, rev):
+    def flush(self, ctx):
+        rev = ctx.rev()
         if rev in self.header:
             h = self.header[rev]
             if h != self.lastheader:
@@ -2156,7 +2157,7 @@
         lines = displayer.hunk.pop(rev).split('\n')
         if not lines[-1]:
             del lines[-1]
-        displayer.flush(rev)
+        displayer.flush(ctx)
         edges = edgefn(type, char, lines, seen, rev, parents)
         for type, char, lines, coldata in edges:
             graphmod.ascii(ui, state, type, char, lines, coldata)

--- a/mercurial/commands.py	Sat Jul 04 17:19:49 2015 +0900
+++ b/mercurial/commands.py	Sun Apr 12 21:52:02 2015 +0900
@@ -4627,7 +4627,7 @@
         else:
             revmatchfn = None
         displayer.show(ctx, copies=copies, matchfn=revmatchfn)
-        if displayer.flush(rev):
+        if displayer.flush(ctx):
             count += 1
 
     displayer.close()