1. wxTimer::Start() returns bool in wxGTK too (other minor corrections

1. wxTimer::Start() returns bool in wxGTK too (other minor corrections
   to this class, such as "const" addition, Notify() is = 0 now...)

2. wxGTK::wxTextCtrl::Delete renamed to Clear for consistency

3. wx/wx_prec.h now includes wx/setup.h even if !wxUSE_PRECOMP because
   otherwise (recently added) tests "#if wxUSE_IOSTREAMH" donb't work.

4. Other compilation fixes for wxGTK (now it compiles again)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@819 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775