Bugfix: proxy: Add missing unistd.h include
FTDI scan: Use intptr_t to avoid warning about different size type cast
Merge commit '91f009a' into bfgminer-3.5.x

Conflicts:
	driver-proxy.c
Merge commit 'f506060' into bfgminer-3.5.x
Bump version to 3.5.3