`py-beginning-of-block-current-column', new command

  "Reach the beginning of block which starts at current column "

New 

(defconst py-block-keywords "\\_<\\(def\\|class\\|if\\|else\\|elif\\|while\\|for\\|try\\|except\\|finally\\|with\\)\\_>"
  "Matches known keywords opening a block. ")
py-indent-line when indent-for-tab-command eq complete, lp:1247340

If `tab-always-indent' is set to 'complete, it completes if max
indent is reached. However cycling won't work than.
py-indent-line, skip-syntax-forward fixed, lp:1247340