Merge branch 'detect-prolog' of https://github.com/tautologico/linguist into tautologico-detect-prolog

Conflicts:
	lib/linguist/blob_helper.rb
	test/test_blob.rb

lib/linguist/languages.yml

@@ -590,6 +590,12 @@ Perl:
   - .perl
   - .psgi
 
+Prolog:
+  major: true
+  extensions:
+  - .pro
+  - .prolog
+
 Pure Data:
   major: true
   lexer: Text only