Pyrex merge: disable multiple compilation in one context, verbose mode to output file names during compilation

--HG--
rename : tests/compile/varargdecl.pyx => tests/run/varargdecl.pyx

use PyBytes_Type instead of PyString_Type in the generated sources, PyBytes fix for Py2.6, unicode fixes for star imports

Make TreeFragment.py more readable; copy substitution nodes and copy over pos attributes on substitutions

'#define PyString_Type PyBytes_Type' in Py3: 'str' is considered a builtin and internally mapped to PyString_Type, which must also work in Py3