Implement Kernel.fail and Kernel#fail .
OP_ENTER fix variable assignment
Move Kernel#fail definition to mruby-kernel-ext mrbgem.
Add mruby-kernel-ext to default gembox.
Merge pull request #2205 from ksss/proc-m2

OP_ENTER fix variable assignment
Merge pull request #2204 from take-cheeze/kernel_fail

Implement Kernel.fail and Kernel#fail .
Fix build on mingw32/64: struct timeval isn't defined in default. See: 642477ef6a92c553d7abb00051674f4b518046c3
Merge pull request #2206 from mattn/fix_build_mingw

Fix build on mingw32/64: struct timeval isn't defined in default. See: 6...
Remove `Time` defined check in test.
Merge pull request #2207 from take-cheeze/time_def

Remove `Time` defined check in mruby-time gem test.
Make Array#[]= raise IndexError.

If second param is negative, Array#[] raise IndexError.
Replace from include <>, to include "".
Merge pull request #2208 from yui-knk/array-error

Make Array#[]= raise IndexError.
Merge pull request #2209 from yui-knk/fix-include

Replace from include <>, to include "".
use mrb_field_write_barrier_value() in array.c
use mrb_field_write_barrier_value() in hash.c
fix typo
Merge pull request #2210 from yui-knk/fix-typo

fix typo
Merge branch 'master' into iij