Small code mistake

Hi there.

I have found small code mistake that cause warnings.
File profiler_api.inc, function profiler_install_users()

There is explode presented and it may receive array parameter instead of string.
You will get next error:

Warning: explode() expects parameter 2 to be string, array given in profiler_install_users() (line 395 of profiler_api.inc).

To reproduce this error you should add user without roles to .info file.
For example:

users[test][uid]    = 20
users[test][name]   = username
users[test][mail]   = example@example.com
users[test][status] = 1

Small patch that fix it attached.

Cheers.