gio: Add SystemTap and DTrace probes for GTask

This adds a basic tapset for GIO, covering various interesting parts of
GTask.

https://bugzilla.gnome.org/show_bug.cgi?id=759813

docs/reference/gio/Makefile.am

@@ -51,6 +51,7 @@ IGNORE_HFILES = \
 	gfileattribute-priv.h		\
 	gfileinfo-priv.h		\
 	ghttpproxy.h			\
+	gio_trace.h			\
 	giomodule-priv.h		\
 	gioprivate.h			\
 	giowin32-priv.h			\

docs/reference/glib/running.xml

@@ -310,7 +310,8 @@ Which would print the contents of each widget in a list of widgets.
 <ulink url="http://sourceware.org/systemtap/">SystemTap</ulink> is a dynamic whole-system
 analysis toolkit.  GLib ships with a file <filename>glib.stp</filename> which defines a
 set of probe points, which you can hook into with custom SystemTap scripts.
-See the files <filename>glib.stp</filename> and <filename>gobject.stp</filename> which
+See the files <filename>glib.stp</filename>, <filename>gobject.stp</filename>
+and <filename>gio.stp</filename> which
 are in your shared SystemTap scripts directory.
 </para>