agrep(1): remove duplicated and obsolete imports.

dirent import is the only one which stays in the odd location.

Part of PR bin/53513.

agrep(1): rewrite binary check introduced with recursive search on rev 1.3 to
match more closely grep(1) implementation. Instead of opening and scanning
full file every time, check for the \0 symbol once the file buffer is filled up
for the first time.

Patch fixes stdin, adds binary check for it as well, and works more efficiently
(at the cost of not scanning the full file).

Also original implementation forgot to add break if binary file is detected,
causing duplicate binary matches in the output result.

Due to full file scans on each match instead of once for the specific file,
scans may have been considerably slow.

Fixes PR bin/53513

Needs pullups to netbsd-9,-10.

Thanks for the help from mlelstv and dh in reviewing and finalizing the patch.

mmap MAP_FAILED audit.

Add some patches which were in an older tree, from January 29 2015:

+ add a -r argument to agrep(1) and document it. This has the same
effect as the -r flag to grep(1) - perform a recursive search
through sub-directories.

+ if a match is found in a "binary" file, then do the same as grep(1)
and just print the message that a match was found in the file, without
attempting to print the match in full.

Use __dead

branches: 1.1.1;
Initial revision

mmap MAP_FAILED audit.

Add some patches which were in an older tree, from January 29 2015:

+ add a -r argument to agrep(1) and document it. This has the same
effect as the -r flag to grep(1) - perform a recursive search
through sub-directories.

+ if a match is found in a "binary" file, then do the same as grep(1)
and just print the message that a match was found in the file, without
attempting to print the match in full.

Use __dead

branches: 1.1.1;
Initial revision

Add some patches which were in an older tree, from January 29 2015:

+ add a -r argument to agrep(1) and document it. This has the same
effect as the -r flag to grep(1) - perform a recursive search
through sub-directories.

+ if a match is found in a "binary" file, then do the same as grep(1)
and just print the message that a match was found in the file, without
attempting to print the match in full.

Use __dead

branches: 1.1.1;
Initial revision