divelog: turn owning-pointers into unique_ptr<>s

Since everything is C++ now, we can use unique_ptr<>s. This makes
the code significantly shorter, because we can now use the default
move constructor and assignment operators.

This has a semantic change when std::move()-ing the divelog:
now not the contents of the tables are moved, but the pointers.
That is, the moved-from object now has no more tables and
must not be used anymore. This made it necessary to replace
std::move()s by std::swap()s. In that regard, the old code was
in principle broken: it used moved-from objects, which may work
but usually doesn't.

This commit adds a myriad of .get() function calls where the code
expects a C-style pointer. The plan is to remove virtually all of
them, when we move free-standing functions into the class it acts
on. Or, replace C-style pointers by references where we don't support
NULL.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/ostctools.cpp

@@ -176,6 +176,6 @@ void ostctools_import(const char *file, struct divelog *log)
 	} else {
 		add_extra_data(&ostcdive->dc, "Serial", ostcdive->dc.serial);
 	}
-	record_dive_to_table(ostcdive.release(), log->dives);
-	sort_dive_table(log->dives);
+	record_dive_to_table(ostcdive.release(), log->dives.get());
+	sort_dive_table(log->dives.get());
 }