Use gethrtime() on HP-UX for timers.

HP-UX does not have clock_gettime(CLOCK_MONOTONIC), instead use
platform-specific gethrtime() function.

Thanks to zhongk for this fix.
Correct #include <sys/uio.h> location.

sys/uio.h should be included in amqp_private.h and not amqp.h, it also should
not be protected by a test for the GCC compiler.

This should fix the issue with compiling rabbitmq-c on HP-UX using aCC.

This fixes #183.
FIX: incorrect OOM for 0-len xchg in amqp_consume.

This fixes a bug in amqp_consume where the function would incorrectly return an
OOM condition when a 0-length exchange name was returned.

Fixes #192
Allow INITIAL bufffer and page size configuration

Signed-off-by: Mike Stitt <mikes@spindance.com>
Remove unused INITIAL_DECODING_POOL_PAGE_SIZE def

AMQP_INITIAL_DECODING_POOL_PAGE_SIZE isn't used anywhere in the code. Getting
rid of it.
FIX: Improve invalid frame detection code.

Improve detection of invalid AMQP frame header before allocating frame buffer.

This fixes #187.

Thanks to Mike Stitt <mikes@spindance.com> for the inspiration on this.