Update doc/po4a.conf for recent changes.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Remove *.pot files and ignore them now.

The .pot files can be generated automatically and the files contain
timestamps in their content. They can cause huge conflicts and take huge
space even if you are not a translator.

This commit is a part of improvement discussed on
https://github.com/mozilla/rust/pull/11383 .

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
auto merge of #11427 : omasanori/rust/remove-pot, r=alexcrichton

`doc/po/*.pot` files are generated automatically using `po4a` and they includes timestamps in their content. The files can cause huge conflicts unnecessarily. Also, removing them save disk space if you are not a translator.
librustc: Implement placement `box` for GC and unique pointers.
auto merge of #11055 : pcwalton/rust/placement-box, r=pcwalton

r? @nikomatsakis
Remove the need to count lang items

This solves horrible diffs where all you do is renumber literally everything.
Support impls directly on primitive types.
Add impls for primitive types in libstd

These impls are mostly currently blank, but they will get filled out in the
future with implementations as we remove satellite traits in favor of inherent
methods on primitives.
rustdoc: Render/hyperlink primitive types

This piggybacks on the previous commits to add impls of primitives directly.