1) unify open/io interfaces: no longer distinguish between FileIo /
AFileIo. instead, one FileIo struct is always used; the
provider-specific data is embedded within it. this avoids the need for a
"base class", which is hard to access (f.fc.flags is ugly)
2) rename x_* redirector to xfile_* and move out of vfs_mount into
separate file
3) xfile is now implemented via "virtual functions" (avoids a lot of
boilerplate code)
4) xfile was too closely tied to vfs_mount (used internal fields);
fixed.
remaining lib/res files: made all flag parameters uint (not int) for
consistency
This was SVN commit r3776.