Til, a command language written in D

[Cléber Zavadniak]

Heeey! Fixed it! Thanks to this 2016 thread: 
https://forum.dlang.org/post/o3tvfh$1lvk$1@digitalmars.com

In short:

1. call `dlerror()` to clean up any eventual old error messages 
(just in case);
2. do **not** look into `lh` (the "library handler") to check for 
errors, because it **can** be null even without any error (see 
Jacob Carlborg answer on that thread)
3. after calling `dlopen`, using the result of another call to 
`dlerror()` to check for errors (it should be NULL if everything 
went okay).



Yay! Now I can create modules linked against `libphobos2` shared 
library!

     ldd libtil_exec.so
         ldd (0x7f8ccd0d9000)
         libphobos2-ldc-shared.so.96 => 
/usr/lib/libphobos2-ldc-shared.so.96 (0x7f8cccb6b000)
         libdruntime-ldc-shared.so.96 => 
/usr/lib/libdruntime-ldc-shared.so.96 (0x7f8ccca0e000)
         libunwind.so.1 => /usr/lib/libunwind.so.1 (0x7f8ccc9f7000)
         libc.so => ldd (0x7f8ccd0d9000)