Modify GetSTEPattribute() and MakeDerived() in SDAI_Application_instance

* For issue #232
* Add a new param named `entity`
* Used in generated code to ensure that the correct attr is being marked as derived.
cleanup, mostly in fedex_plus/classes.c
generated code: improve formatting

* also change one warning to print on a single line
generated code: change addAttr type/behavior, fix #240 (diamond inheritance)

* make addAttrs a bool
* invert the sense of its default value ( 0 -> true )
* pass addAttrs on, unmodified
  - duplicate attributes are ignored by STEPattributeList::push()
* also initialize the parent class
int first -> bool first
eliminate unnecessary variable, formatting
generated code: improve formatting some more
travis-ci: don't bother with gcc since clang is faster
Merge pull request #248 from stepcode/review/diamond

Handle diamond inheritance, treat derived attributes correctly