docbookcs: rename .inc to .ent to reflect php/doc-base#331

Author: jordikroon

docbookcs.xml

@@ -27,7 +27,7 @@
   <file>language-snippets.ent</file>
   <directory>entities/</directory>
   <directory>../doc-base/entities/</directory>
-  <file>../doc-base/temp/manual.inc</file>
+  <file>../doc-base/temp/manual.ent</file>
   <file>../doc-base/temp/entities.ent</file>
   <file>../doc-base/temp/file-entities.ent</file>
   <directory>../doc-base/temp/file-entities</directory>