RFA: document a python function

[Tom Tromey <tromey@redhat.com>]

A user noticed that gdb.texinfo does not document the Python function
gdb.default_visualizer.

This patch adds documentation for it.

Please review.

Tom

2010-08-10  Tom Tromey  <tromey@redhat.com>

	* gdb.texinfo (Pretty Printing API): Document
	gdb.default_visualizer.

Index: doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.748
diff -u -r1.748 gdb.texinfo
--- doc/gdb.texinfo	7 Aug 2010 15:00:38 -0000	1.748
+++ doc/gdb.texinfo	10 Aug 2010 18:03:59 -0000
@@ -21156,6 +21156,16 @@
 If the result is not one of these types, an exception is raised.
 @end defop
 
+@value{GDBN} provides a function which can be used to look up the
+default pretty-printer for a @code{gdb.Value}:
+
+@findex gdb.default_visualizer
+@defun default_visualizer value
+This function takes a @code{gdb.Value} object as an argument.  If a
+pretty-printer for this value exists, then it is returned.  If no such
+printer exists, then this returns @code{None}.
+@end defun
+
 @node Selecting Pretty-Printers
 @subsubsection Selecting Pretty-Printers