python-sage s/lib(gap|ecm).so/libsage\1.so/

lib(gap|ecm).so already exists and confuses autotools

also adapt module_list and doctests
cython: allow file extension overrides
add .pyxx to cythonize file extensions
python-sage: move hypellfrob.cpp and planarity.c

need unique names for object code files...
python-sage: move pyx->pyxx (#15039)

(also changing module_list and references)
cliquer: track untracked patches
csage: build system (#14726)
csage: gitignore
csage: unardcode sage-CSI call
csage: gmp vs mpir
reduce cliquer patching (#14349)
pkgconfig package, incomplete
toplevel: move files (#14796-1)

(extra commit, to help git)
toplevel: build system (#14796-2)

- GNUmakefile.am, configure.ac
- autogen.sh
- empty NEWS, AUTHORS, ChangeLog
- move README.txt to README
- find GNU tar
- core module build rules
- gcc check
- newest_version (from install.in)
- skip "prereq" stuff (for now?)
- change variable names to something more useful
- urlgrabber
- wrapper Makefile
- deps.in
- dist helpers (install, make)
- foreign package en/disable (m4)
- ...
toplevel: build system (#14796-2)

- GNUmakefile.am, configure.ac
- autogen.sh
- empty NEWS, AUTHORS, ChangeLog
- move README.txt to README
- find GNU tar
- core module build rules
- gcc check
- newest_version (from install.in)
- skip "prereq" stuff (for now?)
- change variable names to something more useful
- urlgrabber
- wrapper Makefile
- deps.in
- dist helpers (install, make)
- foreign package en/disable (m4)
- ...
toplevel src versioning (experimental)
toplevel simplify package source version (#14792)

just create symlink <pkgdir>src->actual_package_source-version
toplevel: keepbuild option, WIP, see #14792
toplevel build system continued

- package-(un)install
- TODO
- dist environment
- sage-dist-install program
- sage-setup.py wrapper
- decruft-target and package-distcheck
- sort out compiler versions (thanks, Julian)
- simplify deps.in
- dont stage python-sage
- install helper fixes
- distcheck fixes
- some more deps
- sage_python.m4
- fixing env issues
toplevel: .gitignore