Fix installing simple xspec completions on systems with non-GNU sed.

There's no alternation functionality ('\|' or '|') in POSIX BRE.

bash_completion

@@ -1657,7 +1657,7 @@ _filedir_xspec()
     _expand || return 0
 
     # get first exclusion compspec that matches this command
-    xspec=$( sed -ne $'/^complete .*[ \t]'${1##*/}$'\([ \t]\|$\)/{p;q;}' \
+    xspec=$( awk "/^complete[[:space:]]+.*[[:space:]]${1##*/}([[:space:]]|\$)/ { print \$0; exit }" \
         $BASH_COMPLETION )
     # prune to leave nothing but the -X spec
     xspec=${xspec#*-X }