Don't crash if WXPREFIX env. variable is set

Change wxGetInstallPrefix() to return a string instead of const
wxChar*. The latter was incorrectly obtained from a temporary string if
WXPREFIX was set. While it's possible to fix in a backward compatible
manner without changing the function's signature, it's not worth the
effort for something pretty obscure and used mostly internally.

docs/changes.txt

@@ -105,6 +105,8 @@ Changes in behaviour not resulting in compilation errors
 - wxFileDialog::GetPath() and wxFileDialog::GetFilename() now assert and return
   an empty string if called on dialogs with the wxFD_MULTIPLE style.
 
+- wxGetInstallPrefix() now returns wxString.
+
 
 Changes in behaviour which may result in build errors
 -----------------------------------------------------

include/wx/utils.h

@@ -162,7 +162,7 @@ WXDLLIMPEXP_BASE wxLinuxDistributionInfo wxGetLinuxDistributionInfo();
 WXDLLIMPEXP_BASE wxString wxNow();
 
 // Return path where wxWidgets is installed (mostly useful in Unices)
-WXDLLIMPEXP_BASE const wxChar *wxGetInstallPrefix();
+WXDLLIMPEXP_BASE wxString wxGetInstallPrefix();
 // Return path to wxWin data (/usr/share/wx/%{version}) (Unices)
 WXDLLIMPEXP_BASE wxString wxGetDataDir();
 

src/common/utilscmn.cpp

@@ -182,12 +182,12 @@ void wxUsleep(unsigned long milliseconds)
 }
 #endif
 
-const wxChar *wxGetInstallPrefix()
+wxString wxGetInstallPrefix()
 {
     wxString prefix;
 
     if ( wxGetEnv(wxT("WXPREFIX"), &prefix) )
-        return prefix.c_str();
+        return prefix;
 
 #ifdef wxINSTALL_PREFIX
     return wxT(wxINSTALL_PREFIX);