Add wxActivityIndicator control.

This is a simple animated control indicating some program activity.

Provide native GTK+ (for > 2.20) and OS X implementations as well as a generic
one used under MSW.

Update the sample and the documentation.

configure.in

@@ -885,6 +885,7 @@ WX_ARG_FEATURE(markup,      [  --enable-markup         support wxControl::SetLab
 
 dnl please keep the settings below in alphabetical order
 WX_ARG_FEATURE(accel,       [  --enable-accel          use accelerators], wxUSE_ACCEL)
+WX_ARG_FEATURE(actindicator,[  --enable-actindicator   use wxActivityIndicator class], wxUSE_ACTIVITYINDICATOR)
 WX_ARG_FEATURE(addremovectrl, [  --enable-addremovectrl  use wxAddRemoveCtrl], wxUSE_ADDREMOVECTRL)
 WX_ARG_FEATURE(animatectrl, [  --enable-animatectrl    use wxAnimationCtrl class], wxUSE_ANIMATIONCTRL)
 WX_ARG_FEATURE(bannerwindow,[  --enable-bannerwindow   use wxBannerWindow class], wxUSE_BANNERWINDOW)
@@ -6447,6 +6448,10 @@ if test "$wxUSE_ACCEL" = "yes"; then
   USES_CONTROLS=1
 fi
 
+if test "$wxUSE_ACTIVITYINDICATOR" = "yes"; then
+  AC_DEFINE(wxUSE_ACTIVITYINDICATOR)
+fi
+
 if test "$wxUSE_ADDREMOVECTRL" = "yes"; then
   AC_DEFINE(wxUSE_ADDREMOVECTRL)
 fi