Fix an error when calling a method implemented in C by super() with arguments. This fix makes the following code workable:

Expected:

class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => Sat Apr 21 00:00:00 2012

Actual:

class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => can't convert nil into Integer (TypeError)

Conflicts:
	src/vm.c
Fix type checking in `mrb_flo_to_fixnum`.
fix(String) String#[] accepts float; close #2650 #2651

Conflicts:
	src/string.c
Fix: Numeric#step infinite loop.

Conflicts:
	mrblib/numeric.rb