consider the whole line instead of filename/text

Sometimes I find useful to filter the quickfix contents based only on the filename instead of the text.
For example, if the quickfix window contains the following lines:

    /path/x/fileA.cpp|50| <<global>> #include "fileY.h"
    /path/x/fileB.h|50| <<global>> #include "fileY.h"
    /path/x/fileC.cpp|50| <<global>> #include "fileY.h"

If I want only the .h files that contains a given pattern I could try `:QFGrep \.h|`.

But currently this doesn't work because the matching is done against the filename and the text.
I think most users will think they are grepping the lines displayed on the quickfix, so the current form may be a little misleading.