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

We need to use a double call to SCardListReaders() and allocare the
reader list ourselve.