clang warnings: assigning field to itself, etc

clang-8 on FreeBSD prints these warnings, among others:

```
NL_population.cpp:119:16: warning: assigning field to itself [-Wself-assign-field]
    this->name = name;
               ^
SC_versioncontrol.cpp:172:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
```