CCBUG:468708

Previously kdiff3 was plowing ahead and write out an invalid unmerged file.
This behavior pre-dates but was un-masked by recent changes that hide the ui in auto mode.

BUG:469817
FIXED-IN:1.10.3

This prevents stray worker threads from starting in this mode as they aren't needed.

(cherry picked from commit 95c91809)

(cherry picked from commit b07aca6d40554f1223cb180bd556b1e76ebe098d)

With the expection of m_DTWHeight which was flagged by Valigrind this is a pre-emptive messure.

This code block creates an unstable situation inside Qt that is triggered by any call to std::exit
This causes a crash on exit if '--auto' is engaged
QApplication::exec() stablizes Qt but does not return control to the call point.

CCBUG:468708
(cherry picked from commit c67c2e35)

A bug in Qt 5.15.9 causes a crash under certain circumstances if std::exit is used before calling QApplication::exec.
I don't have time to track this down further.

CCBUG:468708
(cherry picked from commit 4e6a2c42)

Diff3LineList::debugLineCheck only works if Align BC is not used
(cherry picked from commit b174b5c3f72127d8f5c1f4503afa80fdbc130f73)

Replaces two duplicate width calulations.

(cherry picked from commit 430622f19edbd03936f1c34b39e53e178f0a2fde)

Don't generate invalid pointerers in recalcWordWrapHelper

BUG:468492
FIXED-IN:1.10.1