make C char* string literals "const" unless specified otherwise

Conflicts:
	CHANGES.rst

gcc older than 4.7. This fixes a recurring Travis build failure.

Use c++0x rather than c++11 for unique_ptr tests

gcc older than 4.7. This fixes a recurring Travis build failure.

fix passing a C string literal into a void* argument (used in "withgil" test): now requires an explicit cast in C++

typo in buffer protocol docs

prevent non-const char* string literals from being interned

respect tristate return values from isinf() functions instead of shadowing them in a "bint" declaration

Add <memory> header to libcpp