ENH: ensure that content changes in coded objects are noticed (#1293)

- for codedFunctionObject and CodedSource the main code snippets
  were not included in the SHA1 calculation, which meant that many
  changes would not be noticed and no new library would be compiled.

  We now allow tracking of the dynamicCodeContext for the coded
  objects and can append to the SHA1 hasher. This should solve the
  previous misbehaviour.