[svn r305] Started support for custom class allocators/deallocators. Allocators with more than one argument still need to be fixed. Removed the LLVM stacktrace code from mars.c. Moved the LLVM based default target detection code from mars.c to llvmhelpers.cpp.

module bug2;
struct Vec { Vec barf() { return Vec(); } }
class test { this(Vec whee) { } }
void main() { Vec whee; new test(whee.barf()); }