Done-with: Christian Kamm

Store the error message in the QTextCharFormat of the extra selection.

Activate the global completion when the the character at the left of the text cursor is a delimiter.

Move code to Foldernavigationwidget as static utilities and use
them from there and from the Project explorer. Fix error message box.
Task-number: QTCREATORBUG-62

The Navigator "called back" to the model in case e.g. the id
of an item changed. This was catched by the WriteLogger, which
lead to an assert.

Fix this by tracking whether we are changing the navigator items
due to a model change, and not reacting to itemChanged signal
in this case.

hoping for better performance. On this occasion, add context menu
containing "Open" and "Choose folder" enabling drive changes on
Windows. Purge remains of QDirModel elsewhere.
Task-number: QTCREATORBUG-62

Task-number: BAUHAUS-120

Yet another quick and dirty hack while waiting for the real binding pass.

potentially reduces the number of file::exists() calls

partly by removing unnecessary calls, partly by providing minimalistic
reimplementations.
this gives a quite incredible performance boost ...

this gives a rather impressive speed boost.
if qmake wasn't trying to be so clever, we could get even more
out of this.

qmake doesn't, either

that way we save the creation of a temporary stringlist

now that we know the size of the entire file, we can use a single fixed
buffer instead of growing one on-demand - in the case where we just read
the file, we can even re-use the file buffer itself.
this should improve performance for files with very many line
continuations, but the practical impact drowns in the noise.
anyway, the code is nicer, as we don't abuse qstring that obviously any
more.

again several percent faster ...

in release mode they expand to nothing ... not so in debug mode.

- nest conditionals properly to avoid unnecessary tests
- avoid usage of QString::append(QChar) to save allocations