Correct htonll macro detection in CMake.

CMake's check_function_exists() only checks for a symbol being defined in a
library, and does not cover the instance where a function may be defined as a
macro a header. Use check_symbol_exists() to check arpa/inet.h header for symbol
existance of htonll.

This fixes #200
Use amqp_cstring_bytes() to specify locale field.
Add properties table merge function.
Add auth failure client capability as default.
Handle connection.close on auth failure.
Move amqp_bytes_equal to amqp_mem.c
Move table-related funcs to amqp_table.c.
Rename amqp_merge_tables to amqp_merge_capabilities.