support freebsd versions without log2 function
Disable implicit integer conversion in mrb_get_args
add some methods to Symbol
remove unused value for mrb_gv_remove
Merge pull request #1535 from matsumoto-r/del_unused_varaiable

remove unused value for mrb_gv_remove
Merge pull request #1534 from skandhas/pr-add-some-symbol-methods

Add some methods to Symbol
define Module#const_missing
better error position display
Set regs to stack on return of const_get calls before use
Merge pull request #1538 from carsonmcdonald/conststackfix

Set regs to stack on return of const_get calls before use
move declarations to the beginning of blocks
Fixnum#succ may overflow
implement Integer#succ in Ruby
implement some Numeric methods in Ruby
move some methods to make floats and integers compatible [mruby special]
modify upto/downto for compatibility
fix #1542
Merge pull request #1543 from Fleurer/issue1542

fix #1542
fix #1544

We have already reserved that register in codegen()'s case NODE_DEF, but
what we care about is actually the previous register. So what we need is
get that register by cursp() after pop(), then recover the reservation
by push().
add a regression for #1544