Add a new load-relative utility
cython to use relative path loader
Use only a single module-loading search path.
Compile fix, if no scheme installed.
Add explicit build dependencies

Because CMake doesn't know how to peer into the guts of
cython pyx and pxd files, and so doesn't know when to rebuild.
Move the default module patsh to util directory
Merge pull request #748 from linas/load

Fix python module load search paths