The NNN_PIPE file gets deleted after spawning a child in NOWAIT mode. Steps:
- open `nnn` with option `-x`
- press `;o` (custom binding) to open fzopen plugin
- press `^J` to select a file; it will spawn plugin `.cbcp` in NOWAIT mode
- when the intermediate child quits, the NNN_PIPE of parent is also deleted

The following changes are made:

- STDOUT and STDIN are redirected to /dev/null when spawning rclone
  rclone blocks and also shows error/warning messages. nnn needs to spawn
  rclone and return without waiting. To avoid the rclone messages from
  corrupting the screen nnn makes the child silent.
  Note: sshfs returns after mount with a proper error code
- prompt only if both sshfs and rclone are installed

* Fallbacks for absent NAME_MAX and PATH_MAX

Certainly NAME_MAX isn't guaranteed to exist and on (some versions of?)
Illumos and SmartOS it doesn't, so provide some reasonably accommodating
fallbacks.

* Smaller limits

* Remove now redundant PATH_MAX definition for Hurd

This reverts commit dbcbaa583c.

Command: make O_PCRE=1 strip

Kind contribution from uno20001:

https://old.reddit.com/r/C_Programming/comments/etavho/file_manager_nnn_needs_help_with_pcre/fffk4wr/

* Experimental PCRE library support

To compile with PCRE install libpcre-dev(el) and run:

cc  -Wall -Wextra -O3 -DPCRE -D_GNU_SOURCE -D_DEFAULT_SOURCE -I/usr/include/ncursesw -I/usr/include -o nnn src/nnn.c -lreadline -lncursesw -ltinfo -lpcre

* Detach process with F_NOWAIT

Co-authored-by: Mischievous Meerkat <engineerarun@gmail.com>

To compile with PCRE install libpcre-dev(el) and run:

cc  -Wall -Wextra -O3 -DPCRE -D_GNU_SOURCE -D_DEFAULT_SOURCE -I/usr/include/ncursesw -I/usr/include -o nnn src/nnn.c -lreadline -lncursesw -ltinfo -lpcre

make command:

make O_STATIC=1 O_NORL=1 strip

Both in light and detail modes we show more characters than in status bar.

This reverts commit 3d98daaf27.

Some normal text was indent a little, which caused to to become a code

This reverts commit 681b22d5c7.

The statvfs man page:
http://man7.org/linux/man-pages/man3/statvfs.3.html

says clearly:

fsblkcnt_t     f_blocks;   /* Size of fs in f_frsize units */

I missed this earlier.

Replaces the following environment variables:
- NNN_USE_EDITOR
- NNN_IDLE_TIMEOUT