[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