revert list of candidate function to a simple list, instead of a theme item list. that was confusing. jeff is right.

defend against theme functions that return arrays or objects. see theme_table_select_header_cell. bad function. bad.

simplify how we collect template suggestions. flip the order of candidates to most specific first, and fix template log. also add more candidates for functions.

move template log to its own module called devel_themer. that module is still not very usable. stand by.