Fix alloc() redefinition warning
Fix backtrace issues regarding OnRuntimeError and fixes2

Print backtrace to a string BEFORE executing OnRuntimeError or printing any
messages with Printf(). This should solve the problem where you get an
incomplete stack trace when using OnRuntimError or fixes2 plugin (because
they both change the state of the AMX before CrashDetect captured active frames
and other information about the error, e.g. array index).
Add natives for getting/printing backtrace

These are:

native GetAmxBacktrace(string[], size = sizeof(string));
native PrintAmxBacktrace();
native GetNativeBacktrace(string[], size = sizeof(string));
native PrintNativeBacktrace();