Add a WX_APPNAME_DATA_DIR hack for wxStandardPaths::GetDataDir().

Applications using wxStandardPaths::GetDataDir() to find their files under
Unix can't be ran without being installed as they look for their data files
under $prefix/share/appname. Make it possible to override this location by
setting WX_APPNAME_DATA_DIR environment variable to allow running them without
installation.

Notice that this shouldn't present any security risk unless the application is
SUID (which would be a very bad idea anyhow).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62337 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/stdpaths.cpp

@@ -191,6 +191,16 @@ wxString wxStandardPaths::GetConfigDir() const
 
 wxString wxStandardPaths::GetDataDir() const
 {
+    // allow to override the location of the data directory by setting
+    // WX_APPNAME_DATA_DIR environment variable: this is very useful in
+    // practice for running well-written (and so using wxStandardPaths to find
+    // their files) wx applications without installing them
+    static const wxString
+      envOverride(getenv("WX_" + wxTheApp->GetAppName().Upper() + "_DATA_DIR"));
+
+    if ( !envOverride.empty() )
+        return envOverride;
+
    return AppendAppInfo(GetInstallPrefix() + wxT("/share"));
 }