wxProcess::open does not work under windows (the process stays in background mode), wxExecute is still used under windows
Minor other changes

eeschema: code cleaning. SCH_ITEM class used for all schematic items in eeschema. Files reorganization.

some code cleaning and comments translations. Added: EDA_Rect::Merge( EDA_Rect & aRect ) (see changelog)

Fixed segfault which occured when open ing the module editor, loading a module, closing it, and opening the module editor again. This was 
caused by prematurely deleting the module editor's m_Pcb pointer, which has the same value (points to the same structure) as 
g_ModuleEditor_Pcb hence should not be 
deleted.