fix bug 262: Compilation error of stdvector_overload test with GCC 4.6 Now our aligned allocator is automatically activatived only when the user did not specified an allocator (or specified the default std::allocator).
fix bug 262: Compilation error of stdvector_overload test with GCC 4.6
Now our aligned allocator is automatically activatived only when the user
did not specified an allocator (or specified the default std::allocator).

pthulhu/eigen,pthulhu/eigen,cjntaylor/eigen,cjntaylor/eigen,cjntaylor/eigen,pthulhu/eigen,cjntaylor/eigen,pthulhu/eigen,pthulhu/eigen