Small bug fix for gtkentry + echo char support

gtk-rao-981206-0.patch fixes one small bug and adds new functionality
necessary to support our Java peers.  The patch was made against the
CVS tree on 1998-12-06.

The small bug fixed is in gtk_entry_set_visibility.  Since its
possible that the characters in the current entry have changed to some
other character (ie. `*') by a call to gtk_entry_set_visibility, it's
necessary to call entry_adjust_scroll after the offsets have been
recomputed.  This is a one line change.

The new functionality portion of the patch allows gtkentry to be
usable for Java's TextField.  Java has the notion of making an entry
visible or invisible, however it also allows the setting of a
character to be echoed when an entry is invisible.  GTK+ is hard coded
to display stars.  The patch adds an ARG_ECHO_CHAR argument that
allows an echo char to be set/get at runtime.  The echo char defaults
to `*'.

Here's a ChangeLog entry:

1998-12-06  Paul Fisher  <rao@gnu.org>

	* gtk/gtkentry.h: (struct _GtkEntry): Add field echo_char.

	* gtk/gtkentry.c: (gtk_entry_set_visibility): Call
	entry_adjust_scroll.
	(ARG_ECHO_CHAR): New argument.
	(gtk_entry_class_init): Use it.
	(gtk_entry_set_arg): Ditto.
	(gtk_entry_get_arg): Ditto.
	(gtk_entry_draw_text): Rename variable stars to echo_chars.
	(gtk_entry_draw_text): Replace references to '*' with 
	entry->echo_char.
	(gtk_entry_insert_text): Ditto.
	(gtk_entry_recompute_offsets): Ditto.
	(gtk_entry_init): Init entry->echo_char to '*'.
	(gtk_entry_set_echo_char): New function.