Documentation for DTrace USDT probes.

Documentation for DTrace USDT probes.

This patch modifies the `Static Probe Points' section on the GDB
manual in order to cover the support for DTrace USDT probes, in
addition to SystemTap SDT probes.

gdb/doc/ChangeLog:

2015-02-17  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* gdb.texinfo (Static Probe Points): Add cindex `static probe
	point, DTrace'.
	(Static Probe Points): Modified to cover DTrace probes in addition
	to SystemTap probes.  Also modified to cover the `enable probe'
	and `disable probe' commands.