add onlyNames config variable for filtering file names

src/sampleconf/recoll.conf

@@ -60,6 +60,13 @@ skippedNames- =
 # list.</brief><descr></descr></var>
 skippedNames+ =
 
+# <var name="onlyNames" type="string>
+# <brief>Regular file name filter patterns</brief>
+# <descr>If this is set, only the file names not in skippedNames and
+# matching one of the patterns will be considered for indexing. Can be
+# redefined per subtree. Does not apply to directories.</descr></var>
+onlyNames =
+
 # <var name="noContentSuffixes" type="string">
 #
 # <brief>List of name endings (not necessarily dot-separated suffixes) for