Recognize inl files as C++

In some projects these kind of files are used for completely inlined
classes, that can be split up in a header and source file automatically.

src/plugins/cppeditor/CppEditor.mimetypes.xml

@@ -133,5 +133,6 @@
         <glob pattern="*.cxx"/>
         <glob pattern="*.c++"/>
         <glob pattern="*.C"/>
+        <glob pattern="*.inl"/>
     </mime-type>
 </mime-info>