Add rake task completion

See http://turadg.aleahmad.net/2011/02/bash-completion-for-rake-tasks/

ruby/rake_completion.bash

@@ -0,0 +1,57 @@
+# bash completion for rake
+#
+# some code from on Jonathan Palardy's http://technotales.wordpress.com/2009/09/18/rake-completion-cache/
+# and http://pastie.org/217324 found http://ragonrails.com/post/38905212/rake-bash-completion-ftw
+# 
+# For details and discussion
+# http://turadg.aleahmad.net/2011/02/bash-completion-for-rake-tasks/
+#
+# INSTALL
+#
+# Place in your bash completions.d and/or source in your .bash_profile
+# If on a Mac with Homebrew, try "brew install bash-completion"
+# 
+# USAGE
+#
+# Type 'rake' and hit tab twice to get completions.
+# To clear the cache, run rake_cache_clear() in your shell.
+#
+
+function _rake_cache_path() {
+  # If in a Rails app, put the cache in the cache dir
+  # so version control ignores it
+  if [ -e 'tmp/cache' ]; then
+    prefix='tmp/cache/'
+  fi
+  echo "${prefix}.rake_t_cache"
+}
+
+function rake_cache_store() {
+  rake --tasks --silent > "$(_rake_cache_path)"
+}
+
+function rake_cache_clear() {
+  rm -f .rake_t_cache
+  rm -f tmp/cache/.rake_t_cache
+}
+
+export COMP_WORDBREAKS=${COMP_WORDBREAKS/\:/}
+
+function _rakecomplete() {
+  # error if no Rakefile
+  if [ ! -e Rakefile ]; then
+    echo "missing Rakefile"
+    return 1
+  fi
+
+  # build cache if missing
+  if [ ! -e "$(_rake_cache_path)" ]; then
+    rake_cache_store
+  fi
+
+  local tasks=`awk '{print $2}' "$(_rake_cache_path)"`
+  COMPREPLY=($(compgen -W "${tasks}" -- ${COMP_WORDS[COMP_CWORD]}))
+  return 0
+}
+
+complete -o default -o nospace -F _rakecomplete rake