Storage engine independent support for column compression.

TINYBLOB, BLOB, MEDIUMBLOB, LONGBLOB, TINYTEXT, TEXT, MEDIUMTEXT, LONGTEXT,
VARCHAR and VARBINARY columns can be compressed.

New COMPRESSED column attribute added:
COMPRESSED[=<compression_method>]

The only supported method currently is zlib. It is not possible to create index over compressed column.
CSV storage engine stores compressed field data uncompressed on disk.
Binary log stores compressed field data compressed on disk.

System variables added:
column_compression_threshold - Minimum column data length eligible for compression.
column_compression_zlib_level - zlib compression level (1 gives best speed, 9 gives best compression).
column_compression_zlib_strategy - The strategy parameter is used to tune the compression algorithm. Use the value DEFAULT_STRATEGY for normal data, FILTERED for data produced by a filter (or predictor), HUFFMAN_ONLY to force Huffman encoding only (no string match), or RLE to limit match distances to one (run-length encoding). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of FILTERED is to force more Huffman coding and less string matching; it is somewhat intermediate between DEFAULT_STRATEGY and HUFFMAN_ONLY. RLE is designed to be almost as fast as HUFFMAN_ONLY, but give better compression for PNG image data. The strategy parameter only affects the compression ratio but not the correctness of the compressed output even if it is not set appropriately. FIXED prevents the use of dynamic Huffman codes, allowing for a simpler decoder for special applications.
column_compression_zlib_wrap - Generate zlib header and trailer and compute adler32 check value. It can be used with storage engines that don't provide data integrity verification to detect data corruption.

Status variables added:
Column_compressions - incremented every time field data is compressed.
Column_decompressions - incremented every time field data is decompressed.