Replace isdigit/isalpha/.../tolower/toupper with glib variants
This fixes warnings about passing signed chars to them (apparently they
are implemented as macros that do array lookups without checks in some
platforms, yay)
Specifically:
functions=isalnum|isalpha|isdigit|isspace|isxdigit|tolower|toupper
sed -ir "s/$functions/g_ascii_&/g" /*.c