examples: Link only with ../libusb/libusb.la and not with -lusb
examples: Link only with ../libusb/libusb.la and not with -lusb

Similar to libusb.git commit 93b0e09d53ed1d177631af9182378492481a790a
http://git.libusb.org/?p=libusb.git;a=commitdiff;h=93b0e09d53ed1d177631af918

Previous _LDFLAGS included both the freshly built libusb in ../libusb
and -lusb, where libtool would usually resolve the latter to an
already-installed libusb library in the system. The extra reference
to a second libusb library may cause failures to build examples
on some platforms and is wrong.

Fixes #135.

BuLogics/libusb-compat-0.1,BuLogics/libusb-compat-0.1,hjelmn/libusb-compat-0.1,BuLogics/libusb-compat-0.1,hjelmn/libusb-compat-0.1