RFR: 8150617: nth_bit and friends are broken

[Stefan Karlsson]

Hi all,

Please review this patch to fix the nth_bit, right_n_bits, and 
left_n_bits macros.
  http://cr.openjdk.java.net/~stefank/8150617/webrev.00

The macros were broken when expressions with low-precedence operators 
were used. For example (in 64 bit JVMs):
   nth_bit(true ? 32 : 64) returns 0x20 instead of 0x100000000
nth_bit(1|2) returns 0x0 instead of 0x8

The fix is to add parentheses around all usages of the macro input 
parameter. I also added some extra parentheses to further disambiguate 
the expression for readers of the code.

I added STATIC_ASSERTS to show the problem, but I can remove them if 
someone thinks they are unnecessary. Tested with JPRT.

Thanks,
StefanK