Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r264436:
Fix some off-by-one errors. The kve_end and rdl_eaddr fields contain the
first address after the end of the map entry and should therefore be
excluded.

MFC r258000:
Consistently add the relocation offset only when the ELF type is not
ET_EXEC. This fixes several problems with the DTrace pid provider not
being able to match probes.

MFC r240040 (rpaulo):
Make sure we visit both symbol sections even if one of them doesn't
exist. This makes it possible to dtrace some C++ programs like devd.

MFC r254177 (rpaulo):
Fix the return value when we found a symbol in .dynstr. This nasty bug was
preventing a lot of symbol lookups in dtruss -s, for example.

MFC r257300:
Fix an off-by-one error when checking whether a given address is within
the extent of a symbol.

MFC r256661 r257222 r257235 r257248 r257298.

MFC r256661:
Fix the libproc build when DEBUG is defined.

MFC r257222:
Clean up the debug printing in libproc a bit. In particular:

* Don't print any error messages to stderr unless DEBUG is defined.
* Add a DPRINTFX macro for use when errno isn't set.
* Print the error string from libelf when appropriate.

MFC r257235:
Remove an incorrect debug printf.

MFC r257248:
Fix the build with gcc.

MFC r257298:
Revert r257248 and fix the problem in a way that doesn't violate style(9).

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Several fixes for libproc:
o return the correct status in proc_wstatus()
o proc_read takes a void *
o correctly allocate the objs structure array

Sponsored by: The FreeBSD Foundation

New version of libproc. Changes are:
* breakpoint setup support
* register query
* symbol to address mapping and vice-versa
* more misc utility functions based on their Solaris counterpart

Also, I've written some test cases.

Sponsored by: The FreeBSD Foundation

Add a process library with some stubs that the DTrace client needs.
These will be fleshed out as part of the DTrace userland tracing
development.

For now, the kernel tracing part of DTrace requires minimal functionality
for this library.

The API for this library is deliberately different from the libproc in
OpenSolaris due to licensing restrictions.