FIX: todo_completion problem with Bash 3.1

Regexp matching changed from 3.1 to 3.2. Make it work for Bash 3.1 by using an intermediate variable, as in 394c4c748a.
Cp. http://tech.groups.yahoo.com/group/todotxt/message/4211

tests/t0100-code-nobacktick.sh

@@ -9,15 +9,8 @@ On failure, it will print each offending line number and line.
 '
 . ./test-lib.sh
 
-backtick_check()
-{
-    sed -n -e 's/\(^\|[ \t]\)#.*//' -e '/`/{' -e '=;p' -e '}' "$@"
-}
-
 test_todo_session 'no old-style backtick command substitution' <<EOF
->>> backtick_check bin/todo.sh
-
->>> backtick_check ../../todo.cfg
+>>> sed -n -e 's/\(^\|[ \t]\)#.*//' -e '/\`/{' -e '=;p' -e '}' "$(which todo.sh)"
 EOF
 
 test_done

todo.cfg

@@ -2,7 +2,7 @@
 
 # Your todo.txt directory
 #export TODO_DIR="/Users/gina/Documents/todo"
-export TODO_DIR=$(dirname "$0")
+export TODO_DIR=`dirname "$0"`
 
 # Your todo/done/report.txt locations
 export TODO_FILE="$TODO_DIR/todo.txt"

todo_completion

@@ -14,14 +14,15 @@ _todo()
         rm depri dp do help list ls listaddons listall lsa listcon  \
         lsc listfile lf listpri lsp listproj lsprj move \
         mv prepend prep pri p replace report shorthelp"
+    local -r MOVE_COMMAND_PATTERN='^(move|mv)$'
 
     local _todo_sh=${_todo_sh:-todo.sh}
     local completions
     if [ $COMP_CWORD -eq 1 ]; then
         completions="$COMMANDS $(eval TODOTXT_VERBOSE=0 $_todo_sh command listaddons) $OPTS"
     elif [[ $COMP_CWORD -gt 2 && ( \
-        "${COMP_WORDS[COMP_CWORD-2]}" =~ ^(move|mv)$ || \
-        "${COMP_WORDS[COMP_CWORD-3]}" =~ ^(move|mv)$ ) ]]; then
+        "${COMP_WORDS[COMP_CWORD-2]}" =~ $MOVE_COMMAND_PATTERN || \
+        "${COMP_WORDS[COMP_CWORD-3]}" =~ $MOVE_COMMAND_PATTERN ) ]]; then
         # "move ITEM# DEST [SRC]" has file arguments on positions 2 and 3.
         completions=$(eval TODOTXT_VERBOSE=0 $_todo_sh command listfile)
     else