Replace a call to abort() with a VTableMissing exception

This makes some scripts crash less when the viewscreen vtable is unavailable,
for example.

library/DataDefs.cpp

@@ -36,6 +36,7 @@ distribution.
 #include "DataDefs.h"
 #include "DataIdentity.h"
 #include "VTableInterpose.h"
+#include "Error.h"
 
 #include "MiscUtils.h"
 
@@ -310,7 +311,7 @@ void virtual_identity::adjust_vtable(virtual_ptr obj, virtual_identity *main)
         return;
 
     std::cerr << "Attempt to create class '" << getName() << "' without known vtable." << std::endl;
-    abort();
+    throw DFHack::Error::VTableMissing(getName());
 }
 
 virtual_ptr virtual_identity::clone(virtual_ptr obj)

library/LuaTypes.cpp

@@ -1086,6 +1086,11 @@ int LuaWrapper::method_wrapper_core(lua_State *state, function_identity_base *id
         std::string tmp = stl_sprintf("Invalid argument; expected: %s", vn ? vn : "?");
         field_error(state, UPVAL_METHOD_NAME, tmp.c_str(), "invoke");
     }
+    catch (Error::VTableMissing &e) {
+        const char *cn = e.name();
+        std::string tmp = stl_sprintf("Missing vtable address: %s", cn ? cn : "?");
+        field_error(state, UPVAL_METHOD_NAME, tmp.c_str(), "invoke");
+    }
     catch (std::exception &e) {
         std::string tmp = stl_sprintf("C++ exception: %s", e.what());
         field_error(state, UPVAL_METHOD_NAME, tmp.c_str(), "invoke");
@@ -1110,6 +1115,10 @@ int Lua::CallWithCatch(lua_State *state, int (*fn)(lua_State*), const char *cont
         const char *vn = e.expr();
         return luaL_error(state, "%s: Invalid argument; expected: %s", context, vn ? vn : "?");
     }
+    catch (Error::VTableMissing &e) {
+        const char *cn = e.name();
+        return luaL_error(state, "%s: Missing vtable address: %s", context, cn ? cn : "?");
+    }
     catch (std::exception &e) {
         return luaL_error(state, "%s: C++ exception: %s", context, e.what());
     }

library/MiscUtils.cpp

@@ -49,6 +49,10 @@ const char *DFHack::Error::InvalidArgument::what() const throw() {
     return "DFHack::Error::InvalidArgument";
 }
 
+const char *DFHack::Error::VTableMissing::what() const throw() {
+    return "DFHack::Error::VTableMissing";
+}
+
 std::string stl_sprintf(const char *fmt, ...) {
     va_list lst;
     va_start(lst, fmt);

library/include/Error.h

@@ -75,6 +75,14 @@ namespace DFHack
 #define CHECK_INVALID_ARGUMENT(expr) \
     { if (!(expr)) throw DFHack::Error::InvalidArgument(#expr); }
 
+        class DFHACK_EXPORT VTableMissing : public All {
+            const char *name_;
+        public:
+            VTableMissing(const char *name_ = NULL) : name_(name_) {}
+            const char *name() const { return name_; }
+            virtual const char *what() const throw();
+        };
+
 
         class DFHACK_EXPORT AllSymbols : public All{};
         // Syntax errors and whatnot, the xml can't be read