Integrate ext/*.

Integrate ext/gmock-waf 0eec1f8.
Integrate ext/libpng-waf ed8470c.
Integrate ext/libsfz 79d8f33.
Integrate ext/libzipxx 8f6c541.
Integrate ext/rezin af3b2b7.
Default to clang.

Fix a host of compiler warnings introduced in the switch.
Merge branch 'integrate' into develop
Compile with --std=c++11.

Integrate ext/gmock-waf b391e0d.
Integrate ext/libpng-waf 85f6656.
Integrate ext/libsfz b558d31.
Integrate ext/libzipxx c8122e1.
Integrate ext/rezin eec2ee7.
Swap SFZ_FOREACH for range-based for.
Swap sfz::scoped_ptr<> for std::unique_ptr<>.
Swap sfz::linked_ptr<> for std::shared_ptr<>.
Merge branch 'cxx11' into develop