moved Write(const wxString&) to .cpp files as they're going to be changed again soon; removed unnecessary casts

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45043 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/file.cpp

@@ -323,6 +323,16 @@ size_t wxFile::Write(const void *pBuf, size_t nCount)
     return iRc;
 }
 
+bool wxFile::Write(const wxString& s, const wxMBConv& conv)
+{
+  const wxWX2MBbuf buf = s.mb_str(conv);
+  if ( !buf )
+      return false;
+
+  const size_t size = strlen(buf); // FIXME: use buf.length() when available
+  return Write(buf, size) == size;
+}
+
 // flush
 bool wxFile::Flush()
 {