Check sum of `ObjectSpace.count_objects` values is twice of total objects count.
(Which is CRuby's behavior.)

Add detection of VC++2010 in build_config.rb

Fix 'make test' fail to build on Windows(MSVC)

Fix ObjectSpace.count_objects document.

Update mruby-head installed on Travis CI

This way other projects can test against it.

Refactor MRuby::Gem::List#check.

* Create mrbgem table before dependencies check.
* Topoligical sort gem list.
* Check circular mrbgem dependency.

add --help option to mruby-config

delete khash member upper_bound

Fix build fail for 'make test' with no mrbgems

Support :T_FIBER in ObjectSpace.count_objects .

test fails when we don't have Enumerator.

Delete member mask and inc

because there can be substituted by n_buckets

Use bool macro KHASH_DEFINE and KHASH_DECLARE