...to be able to find problems like 6e0bdf04
"sal_Bool arg of SetUseImagesInMenus was abused to squeeze '2' through it"
earlier when converting occurrences of sal_Bool to bool.

Restricting this check to function call arguments avoids too much noise while
hopefully still catching all the relevant problems.

(This check partially overlaps the pointertobool check, so implicit conversions
from pointers to bool call arguments will now generate two loplugin warnings,
but that's harmless.)

Change-Id: I0b03b1d1615aaf8bc18e7a84c56fff3ef9903508