. vfs read_only() assumes vnode->v_vmnt is non-NULL, but it can
be NULL sometimes
. e.g. fchmod() on UDS triggered NULL deref; add a check and
add REQ_CHMOD to pfs so unix domain sockets can be fchmod()ded
. add to test56
Change-Id: I83c840f101b647516897cc99fcf472116d762012
Remove old versions of system calls and system calls that don't have
a libc api interface anymore (dup, dup2, creat).
VFS still contains support for old system call numbers for the new stat
system calls (i.e., 65, 66, 67) to keep supporting old binaries built for
MINIX 3.2.1 (prior to the release).
Change-Id: I721779b58a50c7eeae20669de24658d55d69b25b