As discussed in MDL-48636 we currently use a specific behavioural test to determine if a site supports the new password hashing algorithm. This has two problems:

1) There has been suggestions that it is unreliable, see:
https://github.com/ircmaxell/password_compat/issues/10#issuecomment-15032835
2) The test is quite slow, so the result needs to be cached, which adds some extra complexity to the code.

Since Moodle 2.7+ now requires php 5.4 it is reasonable to expect that site's will support the new password hashing scheme. Therefore for version 2.7 and above we can either:

1) Replace the test with a faster and more reliable PHP version check
2) Remove the test altogether and rely on moodle version checks

This is not urgent but would be good thing to tidy up.