printenv,env: quote problematic variables

printenv,env: quote problematic variables

* doc/coreutils.texi (printenvAlwaysQuoted): New macro.
(printenv invocation): Use it.
(env invocation): Use it.
* src/printenv.h: New file.
* src/local.mk (noinst_HEADERS): Add it.
(src_env_SOURCES): Likewise. Group with src_printenv_SOURCES.
(src_printenv_SOURCES): New variable.
* src/printenv.c: Include argmatch.h and printenv.h.
(main): Quote printed variable names and values.
* src/env.c: Include argmatch.h and printenv.h.
(main): Quote printed variable names and values.
* tests/misc/printenv.sh: Add test cases.
* tests/env/env.sh: Likewise. Adjust invalid UTF-8 test cases.
* NEWS: Mention the change in behavior.