* Removed '--no-warn-mismatch' option from Makefile. This option
makes 'ld' to overlook binary objects compatibility.
* Moved $(PLATFORM_LIBS) from the library group (--start-group ...
--end-group) outside of the group. This will make 'ld' to do
_multiple_ search in the library group when resolving symbol
references and do only a _single_ seach in libgcc.a after the group
search.
* Fix stability problems on CPC45 board again.
* Make image detection for diskboot / usbboot / scsiboot more robust
(also check header checksum)