get_maintainer: allow usage outside of kernel tree

Add option '--no-tree' to get_maintainer.pl script to allow using this
script in projects that aren't the Linux kernel if they use the same
format for their MAINTAINERS file. This command is also available in
checkpatch.pl, for example.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Antonio Nino Diaz <[e-mail]>
Cc: Joe Perches <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

scripts/get_maintainer.pl

···
 my $output_rolestats = 1;
 my $output_section_maxlen = 50;
 my $scm = 0;
+my $tree = 1;
 my $web = 0;
 my $subsystem = 0;
 my $status = 0;
···
 		'subsystem!' => \$subsystem,
 		'status!' => \$status,
 		'scm!' => \$scm,
+		'tree!' => \$tree,
 		'web!' => \$web,
 		'letters=s' => \$letters,
 		'pattern-depth=i' => \$pattern_depth,
···
     die "$P: Please select at least 1 email option\n";
 }
 
-if (!top_of_kernel_tree($lk_path)) {
+if ($tree && !top_of_kernel_tree($lk_path)) {
     die "$P: The current directory does not appear to be "
 	. "a linux kernel source tree.\n";
 }
···
   --sections => print all of the subsystem sections with pattern matches
   --letters => print all matching 'letter' types from all matching sections
   --mailmap => use .mailmap file (default: $email_use_mailmap)
+  --no-tree => run without a kernel tree
   --self-test => show potential issues with MAINTAINERS file content
   --version => show version
   --help => show this help information
 
 Default options:
-  [--email --nogit --git-fallback --m --r --n --l --multiline --pattern-depth=0
-   --remove-duplicates --rolestats]
+  [--email --tree --nogit --git-fallback --m --r --n --l --multiline
+   --pattern-depth=0 --remove-duplicates --rolestats]
 
 Notes:
   Using "-f directory" may give unexpected results: