fix access denied error at incremental build
Clean up mrbconf.h

- undef for windows is not used by default so comment it
- casting to the same type is not needed
- parenthesis are not needed for macro attributes separated by commas
- change order of MRB_NAN_BOXING and MRB_INT64 to simplify logic
Merge pull request #864 from nkshigeru/build_for_vc

fix access denied error at incremental build
Merge pull request #865 from brainopia/mrbconf

Clean up mrbconf.h
remove unused HAVE_UNISTD_H altogether; ref #865
better comment description for mrbconf.h configuration
Fix indent
Call compile method to override to memolize instances
Merge pull request #870 from mattn/regexp_compile

Regexp compile
Fix mrb_fix2str() to enable handling some negative values correctly. This fix is based on @cremno's hack. It will fix #869.
Cosmetic changes. Just added empty lines.
Remove a comment at an unsuitable place.
Add a comment.
Fix an underlying bug. flodivmod() will be crashed in case ((y == 0) && ((divp == NULL) || (modp == NULL))).
Cleanup shift operations.
Merge pull request #873 from monaka/pr-cleanup-numeric-20130223

Clean numeric.c up.
Merge pull request #872 from monaka/pr-fix-mrb_fix2str

Fix mrb_fix2str().