We have renamed following Macros to avoid name confusion:

REFS_PER_FRAME --> INTER_REFS_PER_FRAME
(= ALTREF_FRAME - LAST_FRAME + 1)
MAX_REF_FRAMES --> TOTAL_REFS_PER_FRAME
(= ALTREF_FRAME - INTRA_FRAME + 1)

INTER_REFS_PER_FRAME specifies the maximum number of reference frames
that each Inter frame may use.
TOTAL_REFS_PER_FRAME is equal to INTER_REFS_PER_FRAME + 1, which
counts the INTRA_FRAME.

Further, at the encoder side, since REF_FRAMES specifies the maximum
number of the reference frames that the encoder may store, REF_FRAMES
is usually larger than INTER_REFS_PER_FRAME. For example, in the
ext-refs experiment, REF_FRAMES == 8, which allows the encoder to
store maximum 8 reference frames in the buffer, but
INTER_REFS_PER_FRAME equals to 6, which allows each Inter frame may
use up to 6 frames out of the 8 buffered frames as its references.
Hence, in order to explore the possibility to store more reference
frames in future patches, we modified a couple of array sizes to
accomodate the case that the number of buffered reference frames is
not always equal to the number of the references that are being used
by each Inter frame.

Change-Id: I19e42ef608946cc76ebfd3e965a05f4b9b93a0b3