Avoid buffer overflow on max line length by ending string with just one \0.

ok deraadt@
OpenBSD supports mmap() on block special files too.
Cleanup support for legacy mmap flags

Move all legacy MAP_FOO values behind #ifndef _KERNEL and redefine
them to either be aliases for existing flags (e.g., MAP_COPY ->
MAP_PRIVATE) or 0.

Also, add MAP_OLDFOO defines (behind #ifndef _KERNEL) so the kernel
and kdump can remain compatible with current OpenBSD binaries.

ok deraadt
Cleanup ioctl.2 slightly:

- Markup ioctl argument types with Fa
- Be clearer that ioctl arguments are pointers to ints.

Similar changes to follow for manual pages that describe
device-specific ioctl commands.

Discussed with jmc and schwarze.
re-init and init code paths are now more shared, so the getpid()-based
portable code path must handle that; with brent cook
When building a BN on the stack in BN_div(), make sure to initialize all its
fields (i.e. the flags field) before using it. This is currently harmless,
but might not be if we end up invoking other BN functions checking for
constant-time processing requirement in the future.