Remove redundant insert method in serialize.

This seems to cause problems on recent clang, and looks totally
redundant and unused.

The const_iterator version is identical to the vector::const_iterator
one (which is a typedef thereof). Marking it private (instead of
removing) compiles fine, so this version is effectively unused even.
Checkpoints online.
Update Mac icon to BOB's Bitcoin Image
Hard Fork @ block 12,400 dropping difficulty retarget to 36 blocks, down
        from 2016
Testnet port value of 119985 is too long for 'unsigned short', changed
to 'unsigned long' to compensate. Probably doesn't matter as testnet
is disabled.  This fixes the warning, though.

      src/protocol.h:21:22: warning: implicit conversion from 'int' to
          'unsigned short' changes value from 119985 to 54449