loplugin:nullptr

A plugin to warn about and rewrite null pointer constants that are not written
as nullptr (in C++11 code) resp. NULL (in C and C++03 code).  It is not
activated for the following reasons:

* At least the call to

  pImpl->aFmtNms.insert(pImpl->aFmtNms.begin() + nPos, nullptr);

  in svx/source/items/clipfmtitem.cxx would require
  <https://svn.boost.org/trac/boost/ticket/10540> "missing std::nullptr_t
  support in boost/type_traits/is_pointer.hpp" to be fixed first.

* Additions of code that violate the plugin would probably be frequent, causing
  unnecessary grief for those building with plugins enabled.

* It did not find anything interesting, apart from the above Boost bug and the
  mildly interesting 1da153b617b80887680be65c1854ef8080c2e1c9 "Consistently use
  APP_WRITER as an integer, never as a nullptr."

Anyway,

  until make -O -j4 -k check; do make -O -j1 -k check \
    COMPILER_PLUGIN_TOOL=nullptr UPDATE_FILES=all; done

sucessfully executed on a recent master and resulted in

  6798 files changed, 60919 insertions(+), 60919 deletions(-)

Change-Id: I1260227949868e73fcb63fda13d83e79fde685d7