diff -r 7d4747c711a9 -r 18f935b4c05a hgext/pager.py
--- a/hgext/pager.py	Wed Jul 25 19:02:35 2012 +0200
+++ b/hgext/pager.py	Fri Jul 06 18:06:52 2012 -0400
@@ -53,7 +53,35 @@
 
 testedwith = 'internal'
 
-def _runpager(ui, p):
+def _pagerfork(ui, p):
+    if not util.safehasattr(os, 'fork'):
+        sys.stdout = util.popen(p, 'wb')
+        if ui._isatty(sys.stderr):
+            sys.stderr = sys.stdout
+        return
+    fdin, fdout = os.pipe()
+    pid = os.fork()
+    if pid == 0:
+        os.close(fdin)
+        os.dup2(fdout, sys.stdout.fileno())
+        if ui._isatty(sys.stderr):
+            os.dup2(fdout, sys.stderr.fileno())
+        os.close(fdout)
+        return
+    os.dup2(fdin, sys.stdin.fileno())
+    os.close(fdin)
+    os.close(fdout)
+    try:
+        os.execvp('/bin/sh', ['/bin/sh', '-c', p])
+    except OSError, e:
+        if e.errno == errno.ENOENT:
+            # no /bin/sh, try executing the pager directly
+            args = shlex.split(p)
+            os.execvp(args[0], args)
+        else:
+            raise
+
+def _pagersubprocess(ui, p):
     pager = subprocess.Popen(p, shell=True, bufsize=-1,
                              close_fds=util.closefds, stdin=subprocess.PIPE,
                              stdout=sys.stdout, stderr=sys.stderr)
@@ -71,6 +99,15 @@
         os.dup2(stderr, sys.stderr.fileno())
         pager.wait()
 
+def _runpager(ui, p):
+    # The subprocess module shipped with Python <= 2.4 is buggy (issue3533).
+    # The compat version is buggy on Windows (issue3225), but has been shipping
+    # with hg for a long time.  Preserve existing functionality.
+    if sys.version_info >= (2, 5):
+        _pagersubprocess(ui, p)
+    else:
+        _pagerfork(ui, p)
+
 def uisetup(ui):
     if '--debugger' in sys.argv or not ui.formatted():
         return