add .fcgi file with proper shebang as Perl sample

For issue: https://github.com/github/linguist/issues/466

Before:
% ruby -Ilib ./bin/linguist ~/work/mp/trunk/cgi-bin/index.fcgi
/home/cono/work/mp/trunk/cgi-bin/index.fcgi: 14 lines (7 sloc)
  type:      Text
  mime type: text/plain
  language:

After:
% rake -Ilib samples
% ruby -Ilib ./bin/linguist ~/work/mp/trunk/cgi-bin/index.fcgi 
/home/cono/work/mp/trunk/cgi-bin/index.fcgi: 14 lines (7 sloc)
  type:      Text
  mime type: text/plain
  language:  Perl