Simple refactoring of prefix related functions.

Rename the two prefix-in-list funcs so that their usages are clearer.
Also find and replace all the code that essentially does either.

This introduces additional loops in some places, but I think the added
readability and simplicity outweighs the performance degradation, which
should be negligible anyway.

Test: m nothing
Test: TreeHugger
Change-Id: I37e2276ca0c815105ed0031f23c0b1264b480e4f