[255, 255, 255, 255, 255].hash raises "can't convert Float into Integer"

Fix segfault when `eval("__FILE__")` is executed

Fix bug in mruby-test gem (fix #3094)

Add more limitations

  - defined?
  - alias on global variables
  - Operator modification
  - Kernel.binding missing

In an used build path mruby-test wasn't updating mrbtest.c in the
case that the mgem selection was changed. This lead to:
  - a missing reference in case a GEM was removed
  - ignoring all new GEMs added to the build configuration

This fix keeps track of the active gems and demands a rebuild of
mrbtest.c in case that the gem selection changed.

Add toolchain support for OpenWRT

Addition to mruby limitation documentation

Limitations

Fix missing dependency on mruby-print to support 'puts'

Add String#rjust to mruby-string-ext

Fix a typo

su ported ->
supported
  ^

protect NoMethodError from calling to_hash in replace

Fix SEGV by stack extension in mrb_get_args()

mrb_get_args() keeps pointer of the current stack. But address of the
current stack maybe changed by method call.

'i' format character calls #to_i when the argument isn't integer but
has #to_i.

Here is a code that may call #to_i in mrb_get_args():

    case 'i':
      // ...
            default:
              *p = mrb_fixnum(mrb_Integer(mrb, ARGV[arg_i]));
              break;
     // ...

Here is a code #to_i is called:

    class X
      def initialize(i)
        @i = i
      end

      def to_i
        @i
      end
    end

    [][X.new(0), 0] # X#to_i is called

So, mrb_get_args() shouldn't keep pointer and use it. mrb_get_args()
should always refer mrb->ci->stack to use valid address of the current
stack.

Small grammar fix