introduce libcacard/vscard_common.h

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Signed-off-by: Alon Levy <alevy@redhat.com>

v20->v21 changes: (Jes Sorensen review)
 * license set to 2+
 * long comment fixes, remove empty line at eof.
 * add reference to COPYING

v19->v20 changes:
 * checkpatch.pl

v15->v16 changes:

Protocol change:
 * VSCMsgInit capabilities and magic
 * removed ReaderResponse, will use Error instead with code==VSC_SUCCESS.
 * adaded Flush and FlushComplete, remove Reconnect.
 * define VSCARD_MAGIC
 * added error code VSC_SUCCESS.

Fixes:
 * update VSCMsgInit comment
 * fix message type enum
 * remove underscore from wrapping define
 * update copyright
 * updated comments.
 * Header comment updated
 * remove C++ style comment
 * fix comment for VSCMsgError
 * give names to enums in typedefs
