Move value numbering routines and add VALUE_HANDLE code

[Daniel Berlin]

>>
>> Bootstrapped and tested x86 and x86-64 with no regressions.  Dan and
>> Steven, could you folks take a look and make sure I haven't broken
>> anything subtle?  There should be no behavioural change in PRE.
>>
> It looks fine to me.  I'll give it a try on my local PRE tests (which 
> are unfortunately too large to put in the testsuite) and make sure 
> nothing subtle broke.  Shouldn't be more than an hour or two
>
>
I get exactly the same number of eliminations, etc.
So the code is good to go :)