Merge pull request #2123 from take-cheeze/mrb_int_arg

Use mrb_int in mrbgem rest arguments getting.
Merge pull request #2125 from suzukaze/add-array-keep_if

Add Array#keep_if
should use plain int for index, since i may be printed using %d; close #2127
Merge branch 'master' of github.com:mruby/mruby
Refactoring Comparable
Merge pull request #2128 from mirichi/refactoring-comparable

Refactoring Comparable
mruby-string-utf8: use mrb_int instead of size_t
revert 3644f1b temporary since it caused SEGV only on Travis-CI
Refactor flo_finite_p()
Refactor fix_and()
Refactor fix_or()
Refactor fix_xor()
Merge pull request #2130 from suzukaze/refactor-numeric.c

Refactor numeric.c
check length before calling stack_copy(); based on a patch from @mirich; close #2129
Merge branch 'master' of github.com:mruby/mruby
bit more peephole optimization for NODE_LVAR
The correct is to compare the MRB_STACK_GROWTH.
area of implicit nil is not enough to nregs
Define eval as module function.
Class.constants to take optional argument; close #2133