Fix compiler warning: unused variable 'j'

../src/pcsc-client.cc:109:19: warning: unused variable 'j' [-Wunused-variable]
                unsigned int i, j, k, nbReaders;
                                ^
Use <PCSC/winscard.h> on Mac OS X

Mac OS X uses PCSC as a framework
See http://ludovicrousseau.blogspot.fr/2010/04/pcsc-sample-in-c.html
Use -framework PCSC on Mac OS X
Fix issue #2
SCARD_AUTOALLOCATE is not supported on Mac OS X