Update common.mk

adding CPFLAGS -fPIC for .so generation
Update common.mk

adding CPFLAGS -fPIC for .so generation
Update Makefile

add makefile generation of DeviceProxy_LibUSB.so
Update GadgetFS_helpers.c

adding mount error code
Update PluginManager.cpp

fix .so path
Update Makefile
Update Manager.cpp

fixing compile warning

Manager.cpp: In function ‘void spinner(int)’:
Manager.cpp:251:24: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
Merge pull request #5 from doug2000/master

Merge Doug's fixes to error messages and build