Define filesystem attributes with vfs dependency.

branches: 1.5.2;
Adapt tmpfs_rename to use genfs_rename.

branches: 1.4.8; 1.4.12;
Replace tmpfs_pool custom allocator code with a simpler layer for memory
accounting. Use wired memory (which can be limited) for meta-data, and
kmem(9) for string allocations.

Close PR/31944. Fix PR/38361 while here. OK ad@.

branches: 1.3.2;
Don't generate unused fs_thefs.h headers.

branches: 1.2.18; 1.2.76; 1.2.98;
merge ktrace-lwp.

branches: 1.1.6;
Initial addition of tmpfs, an efficient memory file-system. This project
was developed as part of Google's Summer of Code 2005 program. This
change adds the kernel code, the mount_tmpfs utility, a regression test
suite and does all other related changes to integrate these.

The file-system is still *experimental*. Therefore, it is disabled by
default in all kernels. However, as typically done, a commented-out
entry is added in them to ease its setup.

Note that I haven't commited the required mountd(8) changes to be able
to export tmpfs file-systems because NFS support is still very unstable
and because, before enabling it, I'd like to do some other changes.

OK'ed by my project mentor, William Studenmund (wrstuden@).