commandline: resolve three warnings
commandline: pretty sure this should be a comparison not an assignment
commandline: silence a warning since this is used correctly
commandline: use C automatic stringification
commandline: whitespace
commandline: Makefile use shell assignments to execute once
Backticks in the variables would execute at each invocation.
With Macports, libusb 0.x config is called libusb-legacy-config.
Merge pull request #39 from sodabrew/commandline_warnings

Commandline warnings