1. changed all "wxMBConv& conv" parameters to "const wxMBConv&"

2. this allows to use wxConvAuto() instead of wxConvUTF8 as default value
   for this parameter in the classes which read text from the file: wxConvAuto
   automatically recognizes the BOM at the start of file and uses the correct
   conversion
3. don't use Windows for UTF-7 conversions as there is no way to make it
   fail on invalid UTF-7 strings; use our own wxMBConvUtf7 instead


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38570 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/ffile.h

@@ -18,6 +18,7 @@
 
 #include  "wx/string.h"
 #include  "wx/filefn.h"
+#include  "wx/convauto.h"
 
 #include <stdio.h>
 
@@ -54,14 +55,14 @@ public:
 
   // read/write (unbuffered)
     // read all data from the file into a string (useful for text files)
-  bool ReadAll(wxString *str, wxMBConv& conv = wxConvUTF8);
+  bool ReadAll(wxString *str, const wxMBConv& conv = wxConvAuto());
     // returns number of bytes read - use Eof() and Error() to see if an error
     // occurred or not
   size_t Read(void *pBuf, size_t nCount);
     // returns the number of bytes written
   size_t Write(const void *pBuf, size_t nCount);
     // returns true on success
-  bool Write(const wxString& s, wxMBConv& conv = wxConvUTF8)
+  bool Write(const wxString& s, const wxMBConv& conv = wxConvAuto())
   {
       const wxWX2MBbuf buf = s.mb_str(conv);
       size_t size = strlen(buf);