Fix build fail for 'make test' with no mrbgems
Merge pull request #1997 from kyab/fix-make_test-fail-without-gems

Fix build fail for 'make test' with no mrbgems
downto, upto, step to return Enumerator
add assertion before casting
delete khash member upper_bound
Merge pull request #1998 from ksss/khash-delete-upper_bound

delete khash member upper_bound
Merge branch 'master' of github.com:mruby/mruby
space adjustment in khash.h
add --help option to mruby-config
should not access proc->body.irep if proc is PROC_CFUNC; close #1999
Merge pull request #2000 from kyab/add-help-for-mruby-config

add --help option to mruby-config
add mruby-enum-lazy mrbgem for Enumerable::Lazy
Hash#replace to preserve order; close #2001
protect NoMethodError from calling to_hash in ==/eql?; close #2002
call to_hash before replacing hash
implement Hash#initialize in C
merge test code from #2003
simplify string equality check
Hash#replace should copy default as well; close #2004
backslash escapes in regexp should be addressed by Regexp processor; close #2005