Added a fix for the first part of bug #1355883: make -j2 may cause corruption of Python-ast.h/Python-ast.c. Summary: * Updated asdl_c.py to only generate the interface or the implementation depending on which is given on the command line (e.g. asdl_c.py -h Include Python.asdl will generate Include/Python-ast.h but will not generate Python-ast.c) * Updated Makefile.pre.in to call asdl_c.py with the appropriate arguments. Fix for the second part of this bug here: http://sourceforge.net/tracker/index.php?func=detail&aid=1355940&group_id=5470&atid=305470