Make util.c:flags() stricter -- don't silently ignore unknown flags

Make util.c:flags() stricter -- don't silently ignore unknown flags

* get.c (field_flags_map): Add empty entries for
HAS_FIELD_MARSHAL, HAS_DEFAULT and HAS_FIELD_RVA.
* main.c (method_flags_map): Add empty entry for HAS_SECURITY.
* util.c (flags): Remove known flags from 'code' in loop.  Any
leftover flags are printed as "unknown-flag-xx".

svn path=/trunk/mono/; revision=154432