* src/process.c (Fmake_process): Add new keyword argument
':file-handler'.
(syms_of_process) <make-process, :file-handler>: Define new symbols.
* lisp/files.el (file-name-non-special): Add support for
'make-process'.
* test/src/process-tests.el (make-process/file-handler/found)
(make-process/file-handler/not-found)
(make-process/file-handler/disable): New unit tests.
(process-tests--file-handler): New helper function.
* test/lisp/files-tests.el
(files-tests-file-name-non-special-make-process): New unit test.
* doc/lispref/files.texi (Magic File Names): Document that
'make-process' can invoke file name handlers.
* doc/lispref/processes.texi (Asynchronous Processes): Document
':file-handlers' argument to 'make-process'.
* etc/NEWS (Lisp Changes in Emacs 27.1): Mention new
:file-handler argument for 'make-process'.
* test/src/process-tests.el (process-tests--mixable): New function.
(make-process/mix-stderr): Don’t assume stdout is merged before
stderr. POSIX does not require this, and the assumption failed to
hold on my Fedora 28 platform. See Bug#31214.
* doc/lispref/processes.texi (Asynchronous Processes):
* src/process.c (Fmake_process): Document that standard error is mixed
with standard output if STDERR is nil.
* test/src/process-tests.el (make-process/mix-stderr): New unit test.
* src/process.c (Fmake_process): Have the pipe process honor the
parent's query-on-exit flag.
* test/src/process-tests.el (make-process/noquery-stderr): New test.
Most of this change is to boilerplate commentary such as license URLs.
This change was prompted by ftp://ftp.gnu.org's going-away party,
planned for November. Change these FTP URLs to https://ftp.gnu.org
instead. Make similar changes for URLs to other organizations moving
away from FTP. Also, change HTTP to HTTPS for URLs to gnu.org and
fsf.org when this works, as this will further help defend against
man-in-the-middle attacks (for this part I omitted the MS-DOS and
MS-Windows sources and the test tarballs to keep the workload down).
HTTPS is not fully working to lists.gnu.org so I left those URLs alone
for now.
