Merge branch 'master' into win32

Conflicts:
	mrbgem.rake
	src/socket.c
Fix for VS2013
Fix crash on exiting (avoid double closing)
Unfortunately IPPROTO_TCP and IPPROTO_UDP in Windows are defined as enum, so redefine these as macros for 'const.cstub'.
Fix for MRB_INT64 mode
To make Socket#read and Socket#write workable on Windows, use _open_osfhandle() and _get_osfhandle()
Merge remote-tracking branch 'remotes/mattn/win32' into win32

Conflicts:
	src/socket.c
Merge remote-tracking branch 'origin/win32' into win32-fix-for-read-and-write

Conflicts:
	src/socket.c
Merge pull request #1 from sdottaka/win32

make Socket#write and Socket#read workable for Windows