libcacard: initial commit

libcacard emulates a Common Access Card (CAC) which is a standard
for smartcards. It is used by the emulated ccid card introduced in
a following patch. Docs are available in docs/libcacard.txt

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

---

changes from v24->v25:
 * Fix out of tree builds.
 * Fix build with linux-user targets.

changes from v23->v24: (Jes Sorensen review 2)
 * Makefile.target: use obj-$(CONFIG_*) +=
 * remove unrequired includes, include qemu-common before qemu-thread
  * required adding #define NO_NSPR_10_SUPPORT (harmless)

changes from v22->v23:
 * configure fixes: (reported by Stefan Hajnoczi)
  * test a = b, not a == b (second isn't portable)
  * quote $source_path in case it contains spaces
   - this doesn't really help since there are many other places
     that need similar fixes, not introduced by this patch.

changes from v21->v22:
 * fix configure to not link libcacard if nss not found
    (reported by Stefan Hajnoczi)
 * fix vscclient linkage with simpletrace backend
    (reported by Stefan Hajnoczi)
 * card_7816.c: add missing break in ERROR_DATA_NOT_FOUND
    (reported by William van de Velde)

changes from v20->v21: (Jes Sorensen review)
 * use qemu infrastructure: qemu-thread, qemu-common (qemu_malloc
  and qemu_free), error_report
 * assert instead of ASSERT
 * cosmetic fixes
 * use strpbrk and isspace
 * add --disable-nss --enable-nss here, instead of in the final patch.
 * split vscclient, passthru and docs to following patches.

changes from v19->v20:
 * checkpatch.pl

changes from v15->v16:

Build:
 * don't erase self with distclean
 * fix make clean after make distclean
 * Makefile: make vscclient link quiet

Behavioral:
 * vcard_emul_nss: load coolkey in more situations
 * vscclient:
  * use hton,ntoh
  * send init on connect, only start vevent thread on response
  * read payload after header check, before type switch
  * remove Reconnect
  * update for vscard_common changes, empty Flush implementation

Style/Whitespace:
 * fix wrong variable usage
 * remove unused variable
 * use only C style comments
  * add copyright header
  * fix tabulation

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

libcacard: fix out of tree builds
