Add support for Expression Monitor

	* src/dbgengine/nmv-i-debugger.h (Variable::id)
	(Variable::is_morally_root): New methods.
	* src/persp/dbgperspective/ui/varinspectordialog.ui: Add a new
	"add to monitor" button.
	* src/persp/dbgperspective/nmv-vars-monitor.{cc,h}: New file.
	* src/persp/dbgperspective/menus/varsmonitorpopup.xml: New
	description file for the contextual menu.
	* src/persp/dbgperspective/Makefile.am: Add
	nmv-vars-monitor.{h,cc} and varsmonitorpopup.xml to the build
	system.
	* po/POTFILES.in: Add src/persp/dbgperspective/nmv-vars-monitor.cc
	to the list of translatable source files.
	* src/persp/dbgperspective/nmv-var-inspector-dialog.h: Add
	comments.
	(VarInspectorDialog::FunctionalityFlags): New enum.
	(VarInspectorDialog::functionality_mask): New accessors.
	* src/persp/dbgperspective/nmv-var-inspector-dialog.cc
	(VarInspectorDialog::Priv::{add_to_monitor_button,expr_monitor_requested,
	fun_mask}): New members.
	(VarInspectorDialog::Priv::Priv): Initialize new fun_mask member.
	(VarInspectorDialog::Priv::on_do_monitor_button_clicked)
	(VarInspectorDialog::Priv::functionality_mask): New functions.
	(VarInspectorDialog::Priv::build_dialog): Initialize the
	add_to_monitor button.
	(VarInspectorDialog::Priv::on_var_name_changed_signal): Inspect
	button is now controlled by FUNCTIONALITY_EXPR_INSPECTOR flag.
	(VarInspectorDialog::Priv::on_variable_inspected):  Add to monitor
	button is now controlled by FUNCTIONALITY_EXPR_MONITOR_PICKER
	flag.
	(VarInspectorDialog::expr_monitoring_requested)
	(VarInspectorDialog::functionality_mask): New functions.
	(VarInspectorDialog::Priv::on_var_name_changed_signal): Do not
	enable/disable the "add to monitor" button based on the presence
	of an expression/name in the "variable name" entry field.
	(VarInspectorDialog::Priv::on_variable_inspected): Enable the "add
	to monitor" button only when the expression has been inspected.
	(VarInspectorDialog::Priv::on_variable_inspector_cleared): Disable
	the "add to monitor" button when the inspector has been cleared.
	* src/persp/dbgperspective/menus/menus.xml: Add a menu item to
	activate the new variable monitor.
	* src/persp/dbgperspective/nmv-dbg-perspective-default-layout.cc
	(DBGPerspectiveDefaultLayout::append_view): Style cleanup.
	* src/persp/dbgperspective/nmv-variables-utils.h
	(unlink_a_variable_row): New function.
	* src/persp/dbgperspective/nmv-variables-utils.cc
	(update_a_variable_node, ): Add (better) logging.
	(find_a_variable): Likewise.  Remove dead code.
	(unlink_a_variable_row): Add logging.  Add const to last
	argument.
	(update_a_variable): Add logging.  Style cleanup.
	(set_a_variable): Remove dead code. Style cleanup.
	(unlink_a_variable_row): New function.
	(visualize_a_variable): Style cleanup.
	* src/persp/dbgperspective/nmv-dbg-perspective.h (enum
	ViewsIndex::VARS_MONITOR_VIEW_INDEX): New enumerator.
	* src/persp/dbgperspective/nmv-dbg-perspective.cc
	(DBGPerspective::{on_expr_monitoring_requested,get_vars_monitor_view}):
	New functions.
	(DBGPerspective::Priv::vars_monitor): New
	member.
	(DBGPerspective::{on_expr_monitoring_requested,
	on_activate_vars_monitor_view, get_vars_monitor_view}): New
	functions.
	(DBGPerspective::on_going_to_run_target_signal)
	(DBGPerspective::clear_status_notebook): Take a boolean saying if
	we are re-starting the current program or not.  Re-init the
	variable monitor.  Make the former use the latter.
	(DBGPerspective::going_to_run_target_signal): Take a boolean
	saying if we are re-starting the current program or not.
	(DBGPerspective::detach_from_program): Adjust call to clear to
	clear_status_notebook.
	(DBGPerspective::restart_local_inferior): Adjust call to
	DBGPerspective::going_to_run_target_signal.
	(DBGPerspective::execute_program): Remove useless call to
	clear_status_notebook.  Adjust call to
	DBGPerspective::going_to_run_target_signal.
	(DBGPerspective::init_actions): Define a new action
	to activate the variable monitor view.
	(DBGPerspective::add_views_to_layout): Append the variable
	monitor view.
	(DBGPerspective:::inspect_variable): On the
	event of requesting the monitoring of a variable, hook the new
	function DBGPerspective::{on_expr_monitoring_requested.