Fix a total misinterpretation of underscore-prefixed patterns: they're

not supposed to be completely excluded from processing, they're just
supposed to not appear in the nav, styleguide, or view all views. Per http://patternlab.io/docs/pattern-hiding.html

Author: geoffp

core/lib/pattern_engines/pattern_engines.js

@@ -152,8 +152,7 @@
     isPatternFile: function (filename) {
       // skip hidden patterns/files without a second thought
       var extension = path.extname(filename);
-      if(filename.charAt(0) === '.' ||
-         filename.charAt(0) === '_' ||
+      if (filename.charAt(0) === '.' ||
          (extension === '.json' && !PatternEngines.isPseudoPatternJSON(filename))) {
         return false;
       }

test/pattern_engines_tests.js

@@ -71,7 +71,7 @@
         '00-comment-thread.mustache': true,
         '00-comment-thread.fakeextthatdoesntexist': false,
         '00-comment-thread': false,
-        '_00-comment-thread.mustache': false,
+        '_00-comment-thread.mustache': true,
         '.00-comment-thread.mustache': false,
         '00-comment-thread.json': false,
         '00-homepage~emergency.json': true