Drop support of Python 2.4 and 2.5

[degremont]

Clean Shine code, removing all code features which are not compatible with Python 2.6+, in order to start supporting Python 3 in the future.

• [x] except syntax (except Exception as exp)

• [x] drop has_key()

• [x] Replace 'type(...) is' with isinstance()

• [x] several methods now return an iterator instead of a list. This could easily trigger bugs, but hard to catch them.

• [x] Use proper raise syntax for exceptions

Potential optimizations (not mandatory for Python 3)

• Use Python contexts (with statement)

[degremont]

First step is done in e151b96

[degremont]

I'm considering this ticket done. Let's have a dedicated ticket for Python 3 compat patches.