SWTErrors are thrown when something fails internally which
either leaves SWT in an unknown state (eg. the o/s call to
remove an item from a list returns an error code) or when SWT
is left in a known-to-be-unrecoverable state (eg. it runs out
of callback resources). SWTErrors should not occur in typical
programs, although "high reliability" applications should
still catch them.
This class also provides support methods used by SWT to match
error codes to the appropriate exception class (SWTError,
SWTException, or IllegalArgumentException) and to provide
human readable strings for SWT error codes.