Remove multiple definition of RuntimeError.
Use MRB_DUMP_OK instead of 0.
include/mruby/cdump.h: Add new error codes.
src/cdump.h: Use error codes defined in mruby/cdump.h.
silence clang warning
Merge pull request #736 from selman/cmake_warning_fix

silence clang warning
Merge pull request #734 from monaka/pr-error-check-inprovement-in-cdump-and-dump

Error check inprovements in cdump and dump
Merge pull request #732 from masamitsu-murase/remove_multiple_definition_of_RuntimeError

Remove multiple definition of RuntimeError.
wrong condiiton in too many symbols check; #close #731
Merge branch 'master' of github.com:mruby/mruby