- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

MFC 264990, 264994, 265020, 265025:

Call cpu_icache_sync_range() rather than sync_all since we know the range
and flushing the entire icache is needlessly expensive.

Provide a proper armv7 implementation of icache_sync_all rather than
using armv7_idcache_wbinv_all, because wbinv_all doesn't broadcast the
operation to other cores. In elf_cpu_load_file() use icache_sync_all()
and explain why it's needed (and why other sync operations aren't).

Remove cpu_idcache_wbinv_all() from kdb_cpu_trap(), it's no longer needed.

Explain why wbinv_all is SMP-safe when dumping, and add a missing l2 cache
flush. (Either it was missing here, or it isn't needed in the minidump
case. Adding it here seems like the safer path to consistancy.)

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

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

Define KDB_STOPPEDPCB, so that we can access the backtraces of threads running
on other cores.

Flush D and I caches after setting a breakpoint.

Reviewed by: imp
Obtained from: Semihalf

Add kdb_cpu_sync_icache(), intended to synchronize instruction
caches with data caches after writing to memory. This typically
is required to make breakpoints work on ia64 and powerpc. For
those architectures the function is implemented.

Start all license statements with /*-

Implement breakpoints and single stepping on arm.

Obtained from: NetBSD

Import a kdb.h for arm, which contains stubs right now.