Complete r247813:
Use true/false instead of TRUE/FALSE.

Reported by:	attilio
Requested by:	jhb
Fix assertion failure when using userland DTrace probes from
the pid provider on a kernel compiled with INVARIANTS.

sys/cddl/contrib/opensolaris/uts/intel/dtrace/fasttrap_isa.c:
	In fasttrap_probe_pid(), attempts to write to the
	address space of the thread that fired the probe
	must be performed with the process of the thread
	held.  Use _PHOLD() to ensure this is the case.

	In fasttrap_probe_pid(), use proc_write_regs() instead
	of calling set_regs() directly.  proc_write_regs()
	performs invariant checks to verify the calling
	environment of set_regs().  PROC_LOCK()/UNLOCK() around
	the call to proc_write_regs() so that it's invariants
	are satisfied.

Sponsored by:	Spectra Logic Corporation
Reviewed by:	gnn, rpaulo
MFC after:	1 week