enumerate possible fetchdecode failures leading to #UD decoding. TODO: add this info to BX_IA_ERROR as immediate

git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12231 6c8e4198-a580-4521-a02f-c9ae86df1db9
zero masking is not allowed for all forms of vsib, including gather

git-svn-id: svn://svn.code.sf.net/p/bochs/code/trunk@12232 6c8e4198-a580-4521-a02f-c9ae86df1db9