- Copy stable/10@285827 to releng/10.2 in preparation for 10.2-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.2.
- Update default pkg(8) configuration to use the quarterly branch.[1]

Discussed with: re, portmgr [1]
Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r271651, r271719, r272138, r272457, r272845, r275476, r275518, r275614,
r275819, r276176, r278154, r278160, r278339, r279127, r279240, r279491,
r279493, r279856, r283032, r284423, r284426, r284427, r284428

Merge changes to libm from the past 9 months. This includes improvements
to the Bessel functions and adds the C99 function lgammal.

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

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

The cexp() and {,c}{cos,sin}h functions all need to be able to compute
exp(x) scaled down by some factor, and the challenge is doing this
accurately when exp(x) would overflow. This change replaces all of
the tricks we've been using with common __ldexp_exp() and
__ldexp_cexp() routines that handle all the scaling.

bde plans to improve on this further by moving the guts of exp() into
k_exp.c and handling the scaling in a more direct manner. But the
current approach is simple and adequate for now.

Optimize the case of pure imaginary arguments. Calls like this are
common, e.g., in DFT implementations.

Discussed with: bde, kargl

Add cexp() and cexpf().

Reviewed by: bde (earlier version)