Compilation failure should raise exception

[Tormod Landet]

Currently a JIT compilation failure logs a message at INFO level and returns None.

A better behavior would be to raise an exception. The best would be to raise a custom DijitsoError that can be inspected to find the locations of the generated source code file, error file, build directory etc

This becomes more important soon when dolfin.compile_cpp_code will call dijitso with user generated C++ code. Most people probably do iterative development to make their C++ extension module compile cleanly. Better error reporting is hence necessary.

Logging the current INFO message as WARNING and the compiler error as INFO would be nice in addition to the custom Exception