Attribute "opt_layername" lets you arrange to optimize only one layer.
Improve debug info when dumping symbols
Fix subtle optimizer bug -- add_constant and replace_param_value type issues

Both of these methods took void*'s and assumed that the types of the
blind data had to match the known type where it was to be
copied. Unfortunately, there was a particular series of optimization
steps that could lead to these functions being applied to a "A=B"
instruction where A and B differed in type. In the case I was chasing
down, it was a float=int problem, and the int value was just being
memcpy'd rather than properly converted to a float. So I overhauled both
of these methods to handle the float=int, triple=float, and triple=int
cases, as well as more robustly catching any other cases that it fails
to handle.