Fix document. (Use minirake instead of make.)
Modify String#bytes.

It should return non-negative integer.
Add makefile for backward compatibility of shell build processes.
Merge pull request #649 from masamitsu-murase/fix_string_bytes

Modify String#bytes.
Merge pull request #651 from bovi/make-rake

Add Makefile for backward compatibility of shell build processes.
Merge pull request #650 from monaka/pr-fix-document-to-use-minirake

Fix document. (Use minirake instead of make.)
update INSTALL document based on #650; according to #651
possible to specify ENABLE_GEMS=true.
replace "minirake" to "ruby minirake" for non UNIX platforms
Merge pull request #652 from mattn/env_enable_gems

possible to specify ENABLE_GEMS=true.
add 'default' task if not specified.
Merge pull request #654 from mattn/default_task

add 'default' task if not specified.
Before matz merge 12202012
Before matz merge 12202012
add mrb_mod_cv_get
add mrb_cv_get
mrb_mod_cvar_get
add check_cv_name
add test for Module#class_variable_get
refactor mrb_vm_cv_get