Use "" instead of <> for internal includes

some libusbx include files were included with angle brackets, changed to
quotes. Needed to work better in Xcode project
Core: Fix compiler warning

libusb/io.c:1877:35: warning: implicit conversion loses integer precision: 'long' to 'int' [-Wshorten-64-to-32]
        timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);
                   ~ ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

On Mac OS X tv_sec is a __darwin_time_t which is a long, not an int.
Examples: Fix compiler warning

examples/ezusb.c:251:9: warning: implicit conversion loses integer precision: 'unsigned long' to 'unsigned int' [-Wshorten-64-to-32]
                off = strtoul(buf+3, NULL, 16);
                    ~ ^~~~~~~~~~~~~~~~~~~~~~~~