Fix required literal handling and add debug prints.

In particular, if we had an inner literal and were doing a case insensitive
search, then the literals are dropped because we previously only allowed
a single inner literal to have an effect. Now we allow alternations of
inner literals, but still don't quite take full advantage.

grep/src/search.rs

@@ -152,6 +152,7 @@ impl GrepBuilder {
                  .unicode(true)
                  .case_insensitive(self.opts.case_insensitive)
                  .parse(&self.pattern));
+        debug!("regex ast:\n{:#?}", expr);
         Ok(try!(nonl::remove(expr, self.opts.line_terminator)))
     }
 }