Fixed bool <-> Executability confusion and improved typing a bit.

Fixed bool <-> Executability confusion and improved typing a bit.

Passing a value of type Executability to a function expecting a bool worked only
by accident (because of the order of values in the enum). But using boolean
parameters is often a bad idea, anyway, so we use Executability directly.

Just another example why implicit type conversions in C++ are a bad idea... :-P
Review URL: http://codereview.chromium.org/7753001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9013 ce2b1a6d-e550-0410-aec6-3dcde31c8c00