Update to make AES encryption modes selectable

This is a significant update to allow AES encryption modes to be selected on a
per-key basis.  For now, only ECB and CBC (recommended) modes are supported.
The default is ECB modes in order to maintain backwards compatibility with the
older perl version of fwknop and the Crypt::CBC CPAN module.  This will likely
be changed to use CBC mode by default because of its better security
properties.

In the access.conf file on the server side, there is a new configuration
variable "ENCRYPTION_MODE" that controls the mode for the corresponding AES
key.  On the client side, a new command line argument "--encryption-mode"
controls how the client encrypts SPA packets.
added test suite support for CBC mode Rijndael tcp/22 test
added spa-entropy/ directory for measuring entropy across SPA packets
added the ability to encrypt fwknop client plaintext data with openssl
made default openssl encryption mode 'aes-256-ecb'
update display_ctx() to show the entire plaintext data on one line
Re-worked encryption/decryption handling

For SPA packets encrypted with Rjindael, fwknop has always used CBC mode
even though ECB mode is mentioned in a couple of places.  This change makes
more transparent use of block_encrypt() and block_decrypt() to ensure that
the appropriate mode is used.  The default is CBC mode, but others can be
selected as well (-M <mode> for the fwknop client, and ENCRYPTION_MODE in
access.conf for the fwknopd server).
switched CBC mode test (which is the default Rjindael encryption mode) to ECB mode
added --gpg entropy measurement, added sensible gnuplot yrange calculations
updated to not base64 decode encrypted packet data by default (can override with --base64-decode)
minor header addition for spa-entropy.pl
added test suite support for AES CTR, OFB, CFB, and ECB encryption modes
bugfix to ensure that incoming SPA data in AES mode is a multiple of the Rjindael blocksize (16)
updated docs to reference the default AES encryption mode of CBC
ensure CBC is the default symmetric encryption mode
updated to local_spa.key from the test suite directory
bug fix to ensure to pick up proper entropy min/max values
merged minor updates from master
Test suite support for function coverage testing via gcov

Added --enable-profile-coverage to the configure script to have the fwknop
binaries compiled with gcc profiling support in order to see which functions
get executed by the test suite via gcov.  The last test executed by the test
suite under --enable-profile-coverage contains all fwknop functions that
were not executed under the test run (function execution totals are
cumlative).
Bug fix to throw out invalid access.conf SOURCE entries

This commit causes fwknopd to exit whenever an invalid SOURCE entry is seen
such as ":ANY".  Previous to this commit, valgrind threw the following errors
with ":ANY" as an access.conf SOURCE entry:

Invalid read of size 8
   at 0x117695: free_acc_source_list (access.c:512)
   by 0x1177E3: free_acc_stanza_data (access.c:564)
   by 0x117C67: free_acc_stanzas (access.c:654)
   by 0x10E32E: free_configs (config_init.c:106)
   by 0x10D085: main (fwknopd.c:376)
 Address 0x5a80658 is 8 bytes inside a block of size 16 free'd
   at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x116AE0: add_source_mask (access.c:255)
   by 0x116D57: expand_acc_source (access.c:303)
   by 0x117A82: expand_acc_ent_lists (access.c:620)
   by 0x119570: parse_access_file (access.c:1043)
   by 0x10C77E: main (fwknopd.c:193)

Invalid free() / delete / delete[] / realloc()
   at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x1176A8: free_acc_source_list (access.c:514)
   by 0x1177E3: free_acc_stanza_data (access.c:564)
   by 0x117C67: free_acc_stanzas (access.c:654)
   by 0x10E32E: free_configs (config_init.c:106)
   by 0x10D085: main (fwknopd.c:376)
 Address 0x5a80650 is 0 bytes inside a block of size 16 free'd
   at 0x4C2A82E: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x116AE0: add_source_mask (access.c:255)
   by 0x116D57: expand_acc_source (access.c:303)
   by 0x117A82: expand_acc_ent_lists (access.c:620)
   by 0x119570: parse_access_file (access.c:1043)
   by 0x10C77E: main (fwknopd.c:193)

HEAP SUMMARY:
    in use at exit: 8 bytes in 1 blocks
  total heap usage: 1,659 allocs, 1,659 frees, 238,310 bytes allocated