Prevent manual builds in the DKMS source.

Print an instructive error messsage and exit if the `dkms.conf` file
exists when the userland is configured. (ie: `--with-config=user`)

A non-trivial number of people try to rebuild ZoL from the
`/usr/src/zfs` tree, which is modified to better satisfy Debian
packaging policy and contains only the module sources for DKMS.

Regardless, local installations usually break managed installations,
so this autotools test could be further enhanced to check whether
ZFS has a DKMS registration.
Remove the COPYING file.

Resolve this lintian warning by removing the COPYING file:

	W: zfsutils: extra-license-file usr/share/doc/zfsutils/COPYING
	N:
	N:    All license information should be collected in the debian/copyright
	N:    file. This usually makes it unnecessary for the package to install this
	N:    information in other places as well.
	N:
	N:    Refer to Debian Policy Manual section 12.5 (Copyright information) for
	N:    details.
	N:
	N:    Severity: normal, Certainty: possible
	N:

The COPYING file in this project is a place holder that does not
contain the software license, and it is optional for autotools
because the automake template is "foreign".
Remove all upstream init.d components.

The etc/init.d/ components are redundant because the debian/ overlay
bundles init files according to Debian packaging policy.
Remove the upstream dracut component.

The dracut/ component broke deb systems when it first added to the
upstream ZoL repository, had a near-zero download count when it was
fixed, seems to be unmaintained, and is incompatible with the
dracut-005 package that is currently published in Debian and Ubuntu.
Remove userland dist rules.

The `make dist` rule is used to create the DKMS source package, which
does not contain the userland. (eg: Dist --with-config=kernel only.)

For all userland components in each automake template, delete
instances of EXTRA_DIST and change dist_ to nodist_.
Improve the --with-spl error for DKMS systems.

If the SPL module is unavailable, then the operator gets an error
message that does not apply to installations that are mananged by
DKMS. Change the error message to fit apt-get systems.

A better solution would be to implement a dependency model in DKMS,
or to bundle SPL into the ZFS package.
Improve the SPL version error for DKMS systems.

During kernel package upgrades, if DKMS tries to build the ZFS
modules before the SPL module, then the operator gets an error
message that does not apply to installations that are mananged by
DKMS. Change the error message to fit apt-get systems.

A better solution would be to implement a dependency model in DKMS,
or to bundle SPL into the ZFS package.

Closes: dajhorn/pkg-zfs#30
Add zvol_inhibit_dev module option.

ZoL can create more zvols at runtime than can be configured during
system start, which hangs the init stack at reboot.

When a slow system has more than a few hundred zvols, udev will
fork bomb during system start and spend too much time in device
detection routines, so upstart kills it.

The zfs_inhibit_dev option allows an affected system to be rescued
by skipping /dev/zd* creation and thereby avoiding the udev
overload. All zvols are made inaccessible if this option is set, but
the `zfs destroy` and `zfs send` commands still work, and ZFS
filesystems can be mounted.