Add ~ processing in env vars.

Fixes https://gitlab.com/kicad/code/kicad/issues/1829

(cherry picked from commit 3a9746c657)

common/common.cpp

@@ -469,6 +469,11 @@ wxString KIwxExpandEnvVars(const wxString& str)
         }
     }
 
+#ifndef __WINDOWS__
+    if( strResult.StartsWith( "~" ) )
+        strResult.Replace( "~", wxGetHomeDir(), false );
+#endif // __WINDOWS__
+
     return strResult;
 }