Make GetCurrentInstruction() handle for (;;) statements

Previously completion for lines like: for (i=1; $i<42; ++$i) $foo->
was handled incorrectly by adding the "++$i) " too to the current instruction
while it should have been only "$foo->". It's fixed by counting parenthesis
and collect the whole "for(;;)" just to be cleaned up later.
Merge branch 'master' into my-develop