forward declaration is sufficient.

Dependencies between projects can now be edited in the Projects mode.
You can simply check for each project the projects that it depends on,
and they will be built first. A message box pops up when you try to
create a circular dependency.

Could use some testing.

Task:     241374
Details:  Clean up what we leave behind, take care to not remove anything else. We run make distclean and remove the files we copies there plus the debug and release directories.

Task:     - 238352
Details:  - Since a while now, pro and pri files are directly part of a
project's file list.

RevBy:    con, hjk

Task:     Found by Roberto.

Task:     -
RevBy:    -
AutoTest: -
Details:  Add the include path for qplatformdefs.h to the fot.

Details:  Free the whole ProFile*, ProItem*, ProValue* and etc
structure after parsing, that frees around 200Mb for projects.pro.

Details:  ProFileCache be gone, as is ManagedProFile, not to be missed.
Drastically simplified how ownership works.