Handle bignum overflow immediately in primitive
Add benchmarks for Float operations
Remove fast math instruction specialization

This actually causes more performance degrations than the advantages it
has. Float operations suffer most from these changes and rather than
changing these specialized instructions for floats, we remove them all
together.

Performance of Fixnum handling doesn't seem to suffer from this change
and the JIT can optimize the regular send() path just as well as these
specialized instructions.
Improved version of the write barrier

In the common case of either setting a non reference value or setting a
variable on a young object, we don't have to call a method but check
this inline. This improves performance for these cases where we don't
need to store an object in the write barrier.
Increase default maximum size of normal methods

This helps in JIT'ing methods where the JIT profile changed because of
now treating + as a regular method. One example here is String#+ which
now can be inlined and benefits from larger maximum sizes.