create_convert_utility_code() in PyrexTypes needs a rewrite

[scoder]

Currently, the create_convert_utility_code() methods in PyrexTypes are used to generate utility functions on the fly. However, this is done at type analysis time, not at code generation time. As things like temp allocation, utility code injection and constant caching have now moved to code generation time, the code generation at analysis time can no longer depend on anything code related being place. That makes it crash in the current cython-unstable branch.

The methods should be split into one that checks for prerequisites (called at type analysis time) and one that generates the code, which can then be called during normal code generation.

[scoder]

This is required to finish #144.

[dagss]

I might end up doing this (check ticket assignment).

[dagss]

 http://hg.cython.org/cython-unstable/rev/5a66cd8359e8