Fixed VGA reset handler: check if there is a visible bitmap before 
clearing it.


git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@48811 fb15a70f-31f2-0310-bbcc-cdcc74a49acc
Added names to reset handlers to aid debugging.


git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@48812 fb15a70f-31f2-0310-bbcc-cdcc74a49acc
Moved bootflags to a separate file, since other unwanted definitions 
were being pulled into dos/boot.c.


git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@48813 fb15a70f-31f2-0310-bbcc-cdcc74a49acc