Revision 668

+ finally figured out why the tests failed when the python extension libs were
  no longer sym links. The original setup for python extension modules was to
  have sym links in the esys/* directories named, for example escriptcpp.so.
  These would link to the actual libraries libescriptcpp.so. The lib*.so would
  link to each other. When you replaced the symlink with a copy of the lib*.so
  but renamed without the lib you would then get problems. In particular,
  py_tests would suddenly start failing.

  The problem appears (I've not been able to find documentary evidence to this
  case) to be that when, for example, you import bruce, brucecpp.so imports
  lib/libescriptcpp.so (which intialises escript python bits), bruce then
  imports escriptcpp.so (which also initialised escript python bits).

  Whether that is exactly correct or not is of interest but the important bit
  is you appear to get two versions. After thinking about this for a bit and
  reviewing a bunch of other examples of working python modules I noticed a
  pattern. NONE of the other examples ever included more than the python
  wrapper code in the python extension library. Instead they just link to
  the pure C++ library. This would avoid the duplicate load.

  So, I've refactored the code. If you consider escript the pattern in now:
  lib/libescript.so - which has all of escript EXCEPT the python escriptcpp.cpp
  esys/escript/escriptcpp.so - which has ONLY the escriptcpp.cpp and links to
                               lib/libescript.so
  
  Run the tests and low and behold they all pass again.

  Q: Why doesn't this problem occur with sym links?
  A: My guess is that python and the dynamic linker take a look at the actual
     absolute python of libraries to determine if its a "different" library.
     I did fine some discussions that seem to suggest this.

  Q: Why can't you just set LD_LIBRARY_PATH==PYTHONPATH and stick all the
     libs in that directory?
  A: I (in fact we, Peter Hornby was there) tried. With the renaming of the
     python module so it doesn't have a lib prefix you get problems with
     getting the shared libraries to be looked up in LD_LIBRARY_PATH. Do
     the opposite and use lib on the python modules and you have problems
     with windows which doesn't prepend the lib. Various combination
     in between were also tried but you end up in a catch 22 situation so far
     as I could tell

  Please if you know more about the ins and outs of python and shared
  libraries let me know if this isn't true. I'd really like to know if my
  guesses are correct. In any event, the fix is more consistent with the
  patterns I've seen

  Phew! this was a long log message, glad it is on a branch!