python-sage: build system

- BLAS, BLAS2 check
- generate setup.py, module_list.py
- AC_ARG_VAR
- am_check_python_headers
- AM_DEFAULT_EXT globally (?)
- common makefile
  - dependency tracking for cython files
  - some automake global flags
  - some recursive targets
- add all makefiles to AC_OUTPUT
- header checks
  - cliquer/cl.h
  - flint
  - libgap
  - ..
- create dependency dummies for cython
- AC_AUTO_HEADER (reduce cruft in gcc-calls)
- checks
  - jinja2
  - whether cython supports dependencies
  - cliquer/cliquer.h
- as_ac_expand
python-sage: Makefiles
python-sage gen_interpreters.py
python-sage: fix module bound macros
python-sage: move pyx->pyxx (#15039)

(also changing module_list and references)
python-sage: .gitignore update
python-sage: env
python-sage: simplify fplll includedir
python-sage: fix lrcalc includes

(lrcalc will not work without -I/path/to/include/lrcalc anyway)
python-sage: use CONWAY_DATA_DIR
python-sage, cliquer: work without cliquer patching (#14349)
python-sage: optional packages continued
python-sage build system continued
python-sage: SINGULAR_SO instead of hardwired path
python-sage: unhardcode SAGE_MAXIMA_INIT
python-sage: env.py
python-sage: build system continued

python-sage build-system cleanup
python-sage: remove sage-location check

- the check involves hardwird SAGE_LOCAL
- sage-location is no longer used to fix ipython
python-sage: various references to SAGE_DOC_SRC
python-sage: whitelist python2.7 multiprocessing in stackframes test