[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 bug1;
struct Foo { Foo opSub(ref Foo b) { return Foo(); } }
struct Bar { Foo whee; }
void test(ref Bar moo) { Foo nngh; auto plonk = nngh - moo.whee; }
void main() { Bar bar; test(bar); }