tree-wide: fix a pile of lints

This:
- Converts a bunch of C style casts into C++ casts.
- Removes some very silly pointer subtraction code (which is no more or
  less busted on i686 than it began)
- Fixes some "technically UB" that never had to be UB in the first
  place.
- Makes finally follow the noexcept status of the inner function. Maybe
  in the future we should ban the function from not being noexcept, but
  that is not today.
- Makes various locally-used exceptions inherit from std::exception.

Change-Id: I22e66972602604989b5e494fd940b93e0e6e9297

src/libcmd/repl-interacter.cc

@@ -96,7 +96,7 @@ static int listPossibleCallback(char * s, char *** avp)
         return p;
     };
 
-    vp = check((char **) malloc(possible.size() * sizeof(char *)));
+    vp = check(static_cast<char **>(malloc(possible.size() * sizeof(char *))));
 
     for (auto & p : possible)
         vp[ac++] = check(strdup(p.c_str()));