The PyInt conversion functions generate two warnings when compiled under
`gcc -Wall -Wextra`:

1. comparison of unsigned expression < 0 is always false

2. signed and unsigned type in conditional expression

This patch fixes these problems by creating a new temporary variable
`is_unsigned`, which fixes problem 1, and by converting the ternary
return expression into a normal if/else branch, which fixes problem 2.

--HG--
extra : rebase_source : 3512ea980463bae13f30b0d8bd395cabe253e65c

--HG--
extra : rebase_source : 37bb9de5574e1f7b4f288192eaa3c70a2ae350ca

This provides a fast way to check to see the data type of an ndarray.
For example, to check to see if an integer is 64 bits:

    PyArray_TYPE(a) == NPY_UINT64 or PyArray_TYPE(a) == NPY_INT64

--HG--
rename : Cython/Includes/python_string.pxd => Cython/Includes/python_bytes.pxd
rename : Cython/Includes/python_parse.pxd => Cython/Includes/python_getargs.pxd

fix bug 409: use cascaded assignments also for the complete rhs when optimising parallel assignments

detect optimisable IndexNodes assignments in ref-count optimisation, but do not activate them for now