Correct optimization from 3464f5e77f34; add a test.
If there are two (or more) heads that point to the same .hgtags
node, we can safely skip parsing the file in all but the last head.
(In 3464f5e77f34, we were parsing the file in the first head and
skipping all the others.)
% init
% commit
adding 1/base
adding 2/base
% qnew mqbase
% qrefresh
% qdiff
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% patch file contents
mqbase
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qrefresh 1
% qdiff
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% patch file contents
mqbase
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qrefresh . in subdir
% qdiff
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% patch file contents
mqbase
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qrefresh in hg-root again
% qdiff
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% qdiff dirname
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched
% patch file contents
mqbase
diff -r b55ecdccb5cf 1/base
--- a/1/base
+++ b/1/base
@@ -1,1 +1,1 @@ base
-base
+patched
diff -r b55ecdccb5cf 2/base
--- a/2/base
+++ b/2/base
@@ -1,1 +1,1 @@ base
-base
+patched