Add option to disable Optimus DSM (GH-14)

Necessary for one (some?) older laptops like the Lenovo T410s. Usage: put
"options bbswitch skip_optimus_dsm=1" in your modprobe.conf
Linux 3.8 compatibility hack

Since the following commit, the device would not turn off because the power
state is unknown. Until a fix is released in Linux (or until I know what
better to do), I just assume the power state D0.

commit ddc150f7a33ae0c9cb16eaac3641abc00f56316f
Author: Lv Zheng <lv.zheng@intel.com>
Date:   Fri Nov 16 02:46:28 2012 +0100

    ACPI / PM: Add check preventing transitioning to non-D0 state from D3.

    No power transitioning from D3 state up to a non-D0 state is allowed
    so make acpi_device_set_power() fail and complain if such a transition
    is attempted.

    Signed-off-by: Lv Zheng <lv.zheng@intel.com>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
grsec compatibility (GH-48)

The notifier_call member of struct notifier_block cannot be modified on
grsec-patched kernels. Set the pointer on compile-time instead.
Clarify license (GPLv3+)
README: update module options help
Update to version 0.6, update NEWS
Add copyright header (GH-50)
Do not check for nvidia DSM on igd handle

Just in case the integrated video ACPI handle cannot be found. This is a safety
net for those who try bbswitch on an incompatible machine. I do not know any of
such machinees, but it looks good.
Print path to DSM method on execution failure
Update REAMDE.md

Closes GH-28
Fix WARNING on Linux 3.9 (Closes GH-55)

Patch by amonakov. This stops the following error:

    bbswitch: disabling discrete graphics
    ------------[ cut here ]------------
    WARNING: at drivers/pci/pci.c:1393 pci_disable_device+0x84/0x90()
    Hardware name: B7130
    [44B blob data]
    Modules linked in:
     bbswitch(O+) ip_set_hash_ip xt_set ip_set nfnetlink ipt_REJECT xt_recent xt_tcpudp xt_owner nf_conntrack_ipv6 nf_defrag
    Pid: 2653, comm: modprobe Tainted: G           O 3.9.1-1-custom #1
    Call Trace:
     [<ffffffff8103fe60>] warn_slowpath_common+0x70/0xa0
     [<ffffffff8103fedc>] warn_slowpath_fmt+0x4c/0x50
     [<ffffffff8130712c>] ? pci_bus_write_config_word+0x1c/0x20
     [<ffffffff8130d794>] pci_disable_device+0x84/0x90
     [<ffffffffa05b21f6>] bbswitch_off+0xa6/0x1d0 [bbswitch]
     [<ffffffffa0104248>] bbswitch_init+0x248/0x1000 [bbswitch]
     [<ffffffffa0104000>] ? 0xffffffffa0103fff
     [<ffffffff810002da>] do_one_initcall+0x10a/0x160
     [<ffffffff810a8720>] load_module+0x1d40/0x24a0
     [<ffffffff810a4410>] ? store_uevent+0x40/0x40
     [<ffffffff810a8fce>] sys_finit_module+0x7e/0x80
     [<ffffffff815afcc6>] system_call_fastpath+0x1a/0x1f
    ---[ end trace 1b312a60aa1b0ed6 ]---
    pci 0000:01:00.0: Refused to change power state, currently in D0
README: mention kmod, workaround for T410 (Fixes GH-58)
Update to version 0.7, update NEWS
Change license to GPLv2+

The Linux kernel is licensed under GPLv2. As GPLv3 and GPLv2 are incompatible in
some way, just license bbswitch as GPL 2.0 or (at your choice) any latter
version. Note: I wrote all code of bbswith.c, so I am entitled to change the
license and do not need permission from other authors (as there are not any).

Request made by Ludwig Nussel.
Clarify why Buffer is used instead of Package
README.md: Fix Markdown
Merge pull request #71 from TimothyGu/master

README.md: fix indentation of upstart script for enabling graphics on shutdown
acpi-handle-hack: Linux 3.13 compatibility

Just in case this hack is needed in the future.
Linux 3.13 compatibility

Reported by ArchangeGabriel, original patch by tuxoko (Issue
Bumblebee-Project/bbswitch#75)
Update to version 0.8, update NEWS