Shorten long function names in the assembly view.

[rcaputo]

This is an experimental attempt to prevent functions with long call
signatures from wrapping the Assembly view. It's thwarted by the
disassembly also including long call signatures in branch targets.

I briefly considered hacking the disassembler output, but the embedded
syntax highlighting makes that more difficult than I wanted to tackle.
Guess I'll just need to refactor the code I work on to pass structures
around instead. :)

func_length is half R.max_value_length because it was intended to
truncate function names twice: once for the function on every line,
and again for the branch targets. I may take another pass at shortening
the branch targets if they keep bothering me.