pyximport: fix a bug crashing other processes

pyxbuild overwrites .so file contents, corrupting any mmapped code image
loaded. If pyximporting the same module from two different processes, on
Linux this leads to crashes with bus error.

This commit fixes the issue by unlinking the file first. On Linux et
al., this does not change the file contents of any open FDs.  On
Windows, unlinking fails, and we just switch to using a different file
name.
Allow enums in switch statement optimization.
enum switch test
initialise all fields to 0 when using object structs from the freelist

--HG--
extra : rebase_source : 346e99306b247c116d988b58802ed7e7eb62754c
use a couple of branch prediction macros in tp_new() function, just in case

--HG--
extra : rebase_source : 32ab400fc7cf381d2267ae01b3ada7065d706ed2
delete unused file

--HG--
extra : rebase_source : 3998c84c9c2a646d9588103205666d37731c41a7
properly integrate pyximport into setup.py

--HG--
extra : rebase_source : d0e52d3a06b2734287cc30fe9ef9ebd0a641b05a
Don't require the GIL for cdivision(False).
Add datetime.pxd to cython.cpython. Part II
Add new line at the end of file
Fix inline getters for timedelta
Remove no-gil cdivision error test.
Add test for date/time/datetime/timedelta members
Add missing files
Enable GCC atomic builtins on MinGW, disable on -march=i386
add freelist test for exttype with vtable
reduce freelist sizes below the number of created objects
Disallow C++ exception declarations for non-extern functions.
use constant flags to move wraparound/boundscheck evaluation into inlined Get/Set/DelItemInt() utility functions
minor code cleanup