If the certificate path from the supplicant config is not absolute,
we need to make it absolute. When building with a different builddir,
the certificate from the supplicant config is actually in the srcdir,
but the builddir is the current PWD.
The ctype macros (eg, isalnum(), tolower()) are locale-dependent. Use
glib's ASCII-only versions instead.
Also, replace isascii() with g_ascii_isprint(), since isascii()
accepts control characters, which isn't what the code wanted in any of
the places where it was using it.
Always removing wep_tx_keyidx will cause wpa_supplicant.conf being
written even if nothing has been changed. Now it will be removed only
when wep is not used anymore.
nm_utils_hwaddr_ntoa() and nm_utils_hwaddr_aton() are like
ether_ntoa()/ether_aton(), but handle IPoIB too.
nm_utils_hwaddr_atoba() is like _aton() but returns a GByteArray,
since that's what's wanted in many places.
Also remove nm_ether_ntop() and replace uses of it with
nm_utils_hwaddr_ntoa().
