Make _filedir's "fallback to everything" behavior optional, and off by default.

Configuration variable: COMP_FILEDIR_FALLBACK
http://thread.gmane.org/gmane.comp.shells.bash.completion.devel/3357

bash_completion

@@ -571,8 +571,9 @@ _filedir()
         toks+=( $( compgen -f -X "$xspec" -- $quoted ) )
     fi
 
-    # If the filter failed to produce anything, try without it
-    [[ -n "$1" && "$1" != -d && ${#toks[@]} -lt 1 ]] && \
+    # If the filter failed to produce anything, try without it if configured to
+    [[ -n ${COMP_FILEDIR_FALLBACK:-} && \
+        -n "$1" && "$1" != -d && ${#toks[@]} -lt 1 ]] && \
         toks+=( $( compgen -f -- $quoted ) )
 
     [ ${#toks[@]} -ne 0 ] && compopt -o filenames 2>/dev/null

doc/bash_completion.txt

@@ -30,6 +30,11 @@ Environment variables
     remotely checked-out files.  This requires passwordless access to the
     remote repository.  Default is unset.
 
+*COMP_FILEDIR_FALLBACK*::
+    If set and not null, completions that look for filenames based on their
+    "extensions" will fall back to suggesting all files if there are none
+    matching the sought ones.
+
 *COMP_IWLIST_SCAN*::
     If set and not null, `iwconfig` completion will try to complete on
     available wireless networks identifiers.  Default is unset.