- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Use MK_SSP=no after including bsd.own.mk to disable SSP instead of user-knob
WITH[OUT]_SSP to avoid hitting an error if user has WITH_SSP in their
make.conf. Ports now use this knob.

make[7]: "/usr/src/share/mk/bsd.own.mk" line 466: WITH_SSP and
WITHOUT_SSP can't both be set.

This is similar to previous cleanup done in r188895

Approved by: bapt
Reviewed by: jlh (earlier version)
Approved by: re (marius)
MFC after: 1 week

Bring in some userboot changes from the bhyve branch to reduce diffs.

r238966
Bump up the heap size to 1MB. With a few kernel modules, libstand
zalloc and userboot seem to want to use ~600KB of heap space, which
results in a segfault when malloc fails in bhyveload.

r241180
Clarify comment about default number of FICL dictionary cells.

r241153
Allow the number of FICL dictionary cells to be overridden.
Loading a 7.3 ISO with userboot/amd64 takes up 10035 cells,
overflowing the long-standing default of 10000.

Bump userboot's value up to 15000 cells.

Reviewed by: dteske (r238966,241180)
Obtained from: NetApp

Introduce new API to work with disks from the loader's drivers.
It uses new API from the part.c to work with partition tables.

Update userboot's disk driver to use new API. Note that struct
loader_callbacks_v1 has changed.

Fix r223695 to compile on architectures which don't use the MBR scheme; wrap
the MBR support in the common part of the loader in #ifdef's and enable it
only for userboot for now.

Add a version of the FreeBSD bootloader which can run in userland, packaged
as a shared library. This is intended to be used by BHyVe to load FreeBSD
kernels into new virtual machines.