configure.ac: add an autoconf version prerequisite

ax_pthread.m4 uses AS_CASE() which was added in 2.60

Change-Id: Ifafe2271a8814c734a20d24048e9b24925e13077
Merge "configure.ac: add an autoconf version prerequisite"
lossless: Remove unaligned read warning

(typecast uint32 pointer to uint64).
The proposed change is little (0.05%) slower but avoids uint32 to uint64
pointer conversion.

Change-Id: I6b8828077ea1324fabd04bfa7e7439e324776250
make alpha-detection loop in IsKeyFrame() in good x/y order

Change-Id: Ifeeb855e66c7b6b849e8584787dc24e7371b1e67
Merge "make alpha-detection loop in IsKeyFrame() in good x/y order"