build error: ‘memcpy’ was not declared in this scope

using this compiler:
    gcc version 4.4.5 (Debian 4.4.5-8)
    Target: x86_64-linux-gnu

build failed:
```
/home/campr/metacentrum/bob-1.1.3_src/src/ip/cxx/VLDSIFT.cc: In member function ‘void bob::ip::VLDSIFT::operator()(const blitz::Array<float, 2>&, blitz::Array<float, 2>&)’:
/home/campr/metacentrum/bob-1.1.3_src/src/ip/cxx/VLDSIFT.cc:135: error: ‘memcpy’ was not declared in this scope
```

this PR fixes the problem