pager: work around bug in python 2.4's subprocess module (issue3533)
hg v2.2.2 fixed the pager on Windows, but broke it on Python 2.4.
This patch only uses the new behavior if Python >= 2.5 is detected.
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present