Horizontal scrolling used to be taken into account when updating caret
geometry. This is wrong since it may have changed when time comes to
draw the caret. This leads to a situation where the first apparition
of the caret is at a wrong place.
Now the extra horizontal offset is used at drawing time.
Fixes bug #11603.
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.
