DTrace merged ready for 7.1

[John Birrell]

This is a belated heads up to let you know that I have merged DTrace to the releng7
branch in the nick of time before the feature freeze for 7.1.

Those astute mailing list readers will note that the commit message appears to
have gone missing. Well, either the dog ate it or subversion decided that it was
for certain eyes only (and not yours, or mine).

I have added a note to src/UPDATING mentioning this and a link to the 
documentation.

I want 7.1 release to be built with a GENERIC kernel containing not only the DTrace
hooks, but also the CTF data, so I have defaulted the 'make buildkernel' to
turn on CTF generation. If you are building a kernel and modules without the
KDTRACE_HOOKS option, then you should do a 'make WITHOUT_CTF=1 buildkernel' to
avoid generating the CTF data (although that won't hurt).

For all builds other than 'buildkernel', CTF generation is turned off. You don't
need or want it yet.

--
John Birrell