New commands `enable probe' and `disable probe'.

New commands `enable probe' and `disable probe'.

This patch adds the above-mentioned commands to the generic probe
abstraction implemented in probe.[ch].  The effects associated to
enabling or disabling a probe depend on the type of probe being
handled, and is triggered by invoking two back-end hooks in
`probe_ops'.

In case some particular probe type does not support the notion of
enabling and/or disabling, the corresponding fields on `probe_ops' can
be initialized to NULL.  This is the case of SystemTap probes.

gdb/ChangeLog:

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

	* stap-probe.c (stap_probe_ops): Add NULLs in the static
	stap_probe_ops for `enable_probe' and `disable_probe'.
	* probe.c (enable_probes_command): New function.
	(disable_probes_command): Likewise.
	(_initialize_probe): Define the cli commands `enable probe' and
	`disable probe'.
	(parse_probe_linespec): New function.
	(info_probes_for_ops): Use parse_probe_linespec.
	* probe.h (probe_ops): New hooks `enable_probe' and
	`disable_probe'.

gdb/doc/ChangeLog:

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

	* gdb.texinfo (Static Probe Points): Cover the `enable probe' and
	`disable probe' commands.