lib/vpsc: rename bcopy->b_copy

lib/vpsc: rename bcopy->b_copy

bcopy is the name of a deprecated function. Compiling on a system
system that still have the function (for example android) gives an
error like:

```
[...]
Making all in vpsc
make[3]: Entering directory '/data/data/com.termux/files/home/projects/graphviz/build/lib/vpsc'
  CXX      blocks.lo
../../../lib/vpsc/blocks.cpp:158:36: error: too few arguments provided to function-like macro invocation
        vector<Block*> bcopy(begin(),end());
                                          ^
/data/data/com.termux/files/usr/include/strings.h:61:9: note: macro 'bcopy' defined here
        ^
1 error generated.
```

Not using bcopy for vector names in block.cpp fixes this.