Stpl less slicing

Here's another one dependant on #690

The regexes claimed to match "start of line" when in fact, they did not.By using `.search(s, pos=p)` over `.search(s[p:])`, this now works correctly. This allows the special casing of ternary if to be removed.

The previous regex would allow `% if True: foo() end`, the new one requires `% if True: foo(); end`, which seems to be what the old regex intended anyway.