fix deadlock bug in util_abort for very long (C++) function named

the problem is that in function names can become quite long in C++ which lead to a negative number of bytes for the padding which in turn lead to the malloc operation to fail.

BTW: the backtrace would be more readable if the names would be demangled using "__cxa_abi_demangle" (if available, see http://panthema.net/2008/0901-stacktrace-demangled/cxa_demangle.html)