Fix errors caused by stdio.h dependent code.
Support to build on pwd != mruby source root
Reduce sprintf() calls. Remove mrb_int_to_str() and MRB_INT_FORMAT.
Remove commented out code. Remove redundant function calls.
Merge pull request #876 from masuidrive/fixed_build_system

Support to build on pwd != mruby source root
Merge pull request #879 from monaka/pr-remove-redundant-funcalls

Remove commented out code. Remove redundant function calls.
Merge pull request #875 from monaka/pr-enable-building-libmruby-with-DISABLE_STDIO-macro

Fix errors caused by stdio.h dependent code.
Merge pull request #878 from monaka/pr-reduce-sprintf

Reduce sprintf() calls. Remove mrb_int_to_str() and MRB_INT_FORMAT.