toplevel: .gitignore
toplevel build system continued

- dont stage python-sage
- install helper fixes
- distcheck fixes
- some more deps
toplevel: continued

- sage_python.m4
toplevel .gitignore
cython: add -MF switch to write dependency files (#14728)

... and -M -F -D -P
cython: patch: gdb output dir option
sagelib: build system (#14807)

this implements a plain ./configure && make interface for the parts
located in /src
sage-ext: build-system
sage-doc: move files
sage-doc: build system

- SAGE_DOC_SRC
- quick hacks
sage-bin: move files (make templates)
sage-bin: sage-build
sage-bin: sage-spkg.in
sage-bin: sage.in

- config files to SAGE_ETC=@sysconfdir@
sage-bin: cleanup sage
sage-bin: simplify sage-sdist
sage-bin build system

- add environment for build
- SAGE64 maybe incomplete
- remove sage-arch-env
sage-bin: typo
sage-bin: continued
sage-bin: build system