csearch: Add flag (-g) for grouping output by file (a'la ack --group, or git grep --heading) [PATCH]

```
The goal is so that the output is more palatable to the human eyes, compare:

$ csearch Aqyadaya
/home/nazri/perl5/perlbrew/perls/perl-5.14.2/man/man3/Text::SimpleTable.3:\&
$t1\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);
/home/nazri/perl5/perlbrew/perls/perl-5.14.2/man/man3/Text::SimpleTable.3:\&
$t2\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);
/home/nazri/perl5/perlbrew/perls/perl-5.14.2/man/man3/Text::SimpleTable.3:\&
$t3\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);

$ csearch -g Aqyadaya
/home/nazri/perl5/perlbrew/perls/perl-5.14.2/man/man3/Text::SimpleTable.3
\& $t1\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);
\& $t2\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);
\& $t3\->row(\*(Aqfoobarbaz\*(Aq, \*(Aqyadayadayada\*(Aq);

```

Original issue reported on code.google.com by `ayieh...@gmail.com` on 20 Apr 2012 at 1:46

Attachments:
- [csearch-group-by-file.patch](https://storage.googleapis.com/google-code-attachments/codesearch/issue-20/comment-0/csearch-group-by-file.patch)