The removal of duplicates is done in LastCommandsSection::add and uses
the erase-remove idiom for performance.
Most of the patch is a cleanup of GuiCommandBuffer:
* remove history_ member, that was a copy of the session lastcommands
vector. Use instead a wrapper history() around it and a addHistory
wrapper for adding new entries.
* Make sure that there is only one place where commands are added to
history. The code used to maintain a list for interactive editing,
and a list for saving the session. They could be different in terms
of leading/trailing spaces.
* [unrelated] remove command_ member, which is just a copy of
LyXAction list of commmands. Use directly lyxaction instead.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
