cmake: Require libusb 1.0.20 on Linux

Tell users at configure time libusb 1.0.19 does not work.

But do not enforce this on Windows or Mac OSX.

Author: xlz

cmake_modules/FindLibUSB.cmake

@@ -11,11 +11,14 @@ IF(PKG_CONFIG_FOUND)
   IF(DEPENDS_DIR) #Otherwise use System pkg-config path
     SET(ENV{PKG_CONFIG_PATH} "${DEPENDS_DIR}/libusb/lib/pkgconfig")
   ENDIF()
+  SET(MODULE "libusb-1.0")
+  IF(CMAKE_SYSTEM_NAME MATCHES "Linux")
+    SET(MODULE "libusb-1.0>=1.0.20")
+  ENDIF()
   IF(LibUSB_FIND_REQUIRED)
-    PKG_CHECK_MODULES(LibUSB REQUIRED libusb-1.0)
-  ELSE()
-    PKG_CHECK_MODULES(LibUSB libusb-1.0)
+    SET(LisUSB_REQUIRED "REQUIRED")
   ENDIF()
+  PKG_CHECK_MODULES(LibUSB ${LibUSB_REQUIRED} ${MODULE})
 
   FIND_LIBRARY(LibUSB_LIBRARY
     NAMES ${LibUSB_LIBRARIES}

src/libfreenect2.cpp

@@ -298,11 +298,13 @@ class Freenect2Impl
     initialized(false),
     has_device_enumeration_(false)
   {
+#ifdef __linux__
     if (libusb_get_version()->nano < 10952)
     {
       LOG_ERROR << "Your libusb does not support large iso buffer!";
       return;
     }
+#endif
 
     if(managed_usb_context_)
     {