Introduces Adaptable API.

This packs an adapter interface, intended for anything
that wants and needs to expose an adapter interface.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5533 2fea6a4d-a838-0410-917b-93a53c48e9d2
Introduces Textpattern_Password_Hash.

Adaptable password hashing class. By default implements
a PHPass as the hashing provider.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5534 2fea6a4d-a838-0410-917b-93a53c48e9d2