grep: implement -Bn and -Cn

[mknos]

• For -B, context lines before a matching line are saved in a buffer and emptied when a match occurs
• -C can then be added with no extra logic as a shortcut for -A and -B
• The old meaning of -C goes away, but I'm not aware of any other version of grep that had that special count feature
• To test, I modified the file "ar" so it has two consecutive lines matching "this"

%perl grep  -n -C 5 this ar
452-on the command line to ``select'' archive files for an operation, only
453-the first file with a matching name will be selected.
454-
455-The normal use of ar is for the creation and maintenance of libraries
456-suitable for use with the loader (see ld(1)) although it is not
457:this is good
458:restricted to this purpose.
459-
460-=head2 OPTIONS
461-
462-I<ar> accepts the following options:
463-
--
571-Extract the specified archive members into the files named by the
572-command line arguments.  If no members are specified, all the
573-owner and group will be unchanged.  The file access and modifica-
574-tion times are the time of the extraction (but see the -B<o> op-
575-tion).  The file permissions will be set to those of the file
576:when it was entered into the archive; this will fail if the user
577-is not the owner of the extracted file or the super-user.
578-
579-=back
580-
581-I<ar> exits 0 on success, and >0 if an error occurs.
--
596-=head1 COPYRIGHT and LICENSE
597-
598-This program is copyright by dkulp 1999.
599-
600-This program is free and open software. You may use, copy, modify, distribute
601:and sell this program (and any modified variants) in any way you wish,
602-provided you do not restrict others to do the same.
603-
604-=cut
605-

%perl grep  -n -C 1 this ar
456-suitable for use with the loader (see ld(1)) although it is not
457:this is good
458:restricted to this purpose.
459-
--
575-tion).  The file permissions will be set to those of the file
576:when it was entered into the archive; this will fail if the user
577-is not the owner of the extracted file or the super-user.
--
600-This program is free and open software. You may use, copy, modify, distribute
601:and sell this program (and any modified variants) in any way you wish,
602-provided you do not restrict others to do the same.
--

[coveralls]

Pull Request Test Coverage Report for Build 11831906132

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 73.069%

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Totals
Change from base Build 11830326870:	-0.7%
Covered Lines:	350
Relevant Lines:	479

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