This patch solves the problem described in

http://www.parashift.com/c++-faq-lite/templates.html#faq-35.19

("Why am I getting errors when my template-derived-class uses a member it
inherits from its template-base-class?")

by prepending this-> when refering to inherited members in macros.

icc nastily defines __GNUC__ while it does not support all of gcc's
features.

This prevents silent conversion Tiny_vector<double> to Tiny_vector<int> which
led to difficult to spot bugs.