MB-10161 Pass unevenly sized raw types by pointer

Calls that pass the raw_XX raw number types by value, such as
decode_raw48(foo), can emit code that expects to be able to safely do a
read of the next power-of-two size up from whereever foo lives:

=> 0x00007f9dabc17e4b <+91>:    mov    0xa(%rbx),%rdi
   0x00007f9dabc17e4f <+95>:    add    %rax,%r15
   0x00007f9dabc17e52 <+98>:    callq  0x7f9dabc0df80 <couchstore_decode_raw48@plt>

This can cause crashes when trying to read past the end of a structure's
containing buffer.

Change-Id: Idc5bcfe938d6d31e48d89455166c964cdb20493e
Reviewed-on: http://review.couchbase.org/33605
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>