Attempt to make QFile I/O 64-bit safe

Use qint64 wherever possible. The linear buffer is never requested to
allocate that much memory (always limited), but at least we ensure we're
not dropping bits where we shouldn't.

Windows's POSIX compatibility layer is never largefile enabled, so it is
always necessary to chunk large reads and writes. On Unix, this will
be rare, unless someone passed -no-largefile to configure, for some
weird reason.

Unfortunately, this is not testable, unless we can allocate a buffer
with 4 GB or more in size. The test for this would be to open a file we
know to be small, then try to read 4 GB + 1 byte. If everything works
correctly, we'll read the full file; if there was a truncation, we'd
read one byte.

Change-Id: If3ee511bf1de17e0123c85bbcaa463b9972746ce
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Don't always chmod the XDG_RUNTIME_DIR

Since the current user is the owner of the dir, we'll get 0x7700 as
permissions, not just 0x700. With the wrong check, we were always doing
an unnecessary chmod.

Task-number: QTBUG-41735
Change-Id: Ib1fc258fef4bf526baa9c71201f9b78d36f5454f
Reviewed-by: David Faure <david.faure@kdab.com>
Report the system error on why chmod(2) failed in XDG_RUNTIME_DIR

This is a very rare occurrence: if the user is the owner of the
directory, the user can chmod(2), and we already checked that the user
is the owner. However, chmod(2) can still fail on read-only fs and on
hardened systems.

Task-number: QTBUG-41735
Change-Id: I8f8bac763bf5a6e575ed59dac55bd265e5b66271
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: David Faure <david.faure@kdab.com>
Autotest: synchronize with the peer before emitting more signals

Several of the unit tests request that the peer emit more than one
signal, but only handle one. The rest of the signals stay queued in the
socket and will be delivered at the next test, causing it to fail often.

This doesn't happen in the tests with the bus. There, we don't receive
the extraneous signals due to AddMatch/ReceiveMatch on each signal
individually and the synchronous nature of the emission (the signals
have already been emitted by the next AddMatch and cannot match it).

Task-number: QTBUG-42145
Change-Id: I743a0553074972042fca46b76db5d9e7b3209620
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Fix warnings about size conversion in QList

Because difference_type is 64-bit on 64-bit systems, there's a
downconversion warning from MSVC and possibly other compilers when it
gets passed to functions taking simply int.

Task-number: QTBUG-41092
Change-Id: I46a710810f4a57b8b84c4933f419a1f1fdf6bb5a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>