content-sqlite: use BLOB type for hash keys

Problem: CHAR(20) type for hash keys would appear to truncate
sha256 hash keys, and implies that character set encoding/collation
code is used in key comparisons.

It turns out that content-sqlite ignores the CHAR length parameter,
and that character set stuff may be effectively a no-op here - at least
simple tests in #2795 show that it may be equivalent to BLOB in terms
of stored size and comparison overhead.

Anyway, CHAR(20) looks wrong, so change it to BLOB.

Fixes #2795

Author: garlick

src/modules/content-sqlite/content-sqlite.c

@@ -36,7 +36,7 @@ const size_t lzo_buf_chunksize = 1024*1024;
 const size_t compression_threshold = 256; /* compress blobs >= this size */
 
 const char *sql_create_table = "CREATE TABLE if not exists objects("
-                               "  hash CHAR(20) PRIMARY KEY,"
+                               "  hash BLOB PRIMARY KEY,"
                                "  size INT,"
                                "  object BLOB"
                                ");";