`py-beginning-of-clause' fixed

wrong type argument, lp:901541, again

mark commands added

`py-shell-complete' fixed
docu updated
menu, mark forms again
`if-block', `try-block' forms dropped

considered useful in seldom cases only
`py-beginning-of-block' fixed

cursor would jump to the next beginning of block above,
disregard nesting-level, finding the wrong beginning