A method's .check_settings method checks for inconsistent setting files
and prints readable errors so there's no need to do that again in
.load_settings, although at some point after removing the duplicate
error messages from the load_settings methods we agreed to keep minimum
checks that could cause a crash e.g. in a corner case like when the
setting file got modified between the check_settings and the
load_settings call. Some error messages have been re-added to
load_settings after that (e.g. in
bb4e1ebd4f) but they're incomplete and not
useful so remove them.
Switch EAP-MD5 to use the common password setting key nomenclature.
The key name has been changed from PREFIX-MD5-Secret to PREFIX-Password.
Note: The old key name is supported.
In addition, this patch adds an ability to request Identity and/or
Password from user.
Replace usages of l_settings_get_value with l_settings_get_string, which
will make sure the returned strings are unescaped but also allocates
memeory and forces us to use l_free on most of the strings. Some of
these strings we explicitly set with l_settings_set_string() in our code
so when we retrieved them with l_settings_get_value() we would receive a
different string if there were any escapable characters in the string.
I didn't replace any of the l_settings_get_value() uses where we're just
checking whether a setting is present, or those which are hexstrings or
EAP method names assuming that they can't have any special characters,
although this isn't future proof. I did use l_settings_get_string() for
file paths though.
The EAP-method's .probe methods only checked the method name so do that
in eap.c instead and allocate method state in .load_settings. Rename
method's .remove method to .free to improve the naming.
