Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

When decoding SLEB128, make sure sign extension is performed for
64-bit integers.

MFC after: 3 days

Store accurate offset information in CTF data. A large number of
structs had incorrect member offsets, limiting dtrace's usefulness
when working with them. An example of incorrect info (struct
rtentry) from before this fix:

<1738> STRUCT rtentry (200 bytes)
rt_nodes type=1731 off=0
rt_gateway type=849 off=65280 <== WRONG, should be 8 * 96
rt_flags type=3 off=65344 <== wrong again, and so on..
...

Approved by: re (kib), gnn (mentor)
MFC after: 2 weeks

Add a BSD licensed DWARF library for use by the DTrace clients.

The API for this library is deliberately different to the GPL'd
libdwarf to avoid licensing problems.