stream-clone: disable gc for `_entries_walk` duration
The number of small container created turn Python in a gc-frenzy that seriously
impact performance.
This significantly boost performance. The following number comes from a large
private repository using perf::stream-locked-section:
base-line: 35.04 seconds
prev-change: 24.51 seconds (-30%)
this-change: 20.88 seconds (-40% from baseline; -15% from previous changes)
$ hg init a
$ cd a
$ hg diff inexistent1 inexistent2
inexistent1: * (glob)
inexistent2: * (glob)
$ echo bar > foo
$ hg add foo
$ hg ci -m 'add foo'
$ echo foobar > foo
$ hg ci -m 'change foo'
$ hg --quiet diff -r 0 -r 1
diff -r a99fb63adac3 -r 9b8568d3af2f foo
--- a/foo Thu Jan 01 00:00:00 1970 +0000
+++ b/foo Thu Jan 01 00:00:00 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg diff -r 0 -r 1
diff -r a99fb63adac3 -r 9b8568d3af2f foo
--- a/foo Thu Jan 01 00:00:00 1970 +0000
+++ b/foo Thu Jan 01 00:00:00 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg --verbose diff -r 0 -r 1
diff -r a99fb63adac3 -r 9b8568d3af2f foo
--- a/foo Thu Jan 01 00:00:00 1970 +0000
+++ b/foo Thu Jan 01 00:00:00 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg --debug diff -r 0 -r 1
diff -r a99fb63adac3f31816a22f665bc3b7a7655b30f4 -r 9b8568d3af2f1749445eef03aede868a6f39f210 foo
--- a/foo Thu Jan 01 00:00:00 1970 +0000
+++ b/foo Thu Jan 01 00:00:00 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ cd ..