- 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 r259473:

Enable llvm's integrated assembler for PowerPC, since it should now be
good enough for typical usage.

Requested by: rdivacky

Enable llvm's integrated assembler for PowerPC, since it should now be
good enough for typical usage.

Requested by: rdivacky
MFC after: 1 week