manifest: fix possible SEGV caused by uninitialized lazymanifest fields
Before, uninitialized self->pydata would be passed to lazymanifest_dealloc()
on OOM, and Py_DECREF(self->pydata) would crash if we were unlucky.
It's still wrong to do malloc() thingy in tp_init because __init__() may be
called more than once [1], but I don't want to go a step further in stable
branch.
[1]: https://docs.python.org/2/c-api/typeobj.html#c.PyTypeObject.tp_new
"The tp_new function should ... do only as much further initialization as
is absolutely necessary. Initialization that can safely be ignored or
repeated should be placed in the tp_init handler."
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a