Fixed pure ruby mrbgems can't compile and fixed build script wrong variable name
Merge remote-tracking branch 'mruby/master'
Add check for using cdump with DISABLE_STDIO option.
Added gem :github option
Merge pull request #706 from masuidrive/add_gem_github_option

Added gem :github option
Export mrb_ary_clear in array.h
Merge remote-tracking branch 'mruby/master' into array-clear
Merge pull request #707 from bovi/array-clear

Export Array#clear in array.h
Merge pull request #702 from monaka/pr-check-cdump-with-disable-stdio

Add check for using cdump with DISABLE_STDIO option.