Closing up PoW security loophole.

Killed any Proof of Work after Block 30,000 (PoSTakeoverHeight)
Got rid of redundant definition of insert in serialize.h that causes build to fail on some systems
Fixed namespace issue for array in net.cpp that causes build to fail on some systems
Added recent checkpoint and sync checkpoint
Removed unused function be3dec from pbkdf2.cpp
Fixed alignment widht in scrypt-x8_64.S that causes build to fail on some systems
Added obj directory to src so that building goes easier