Support for bad UARTs: added -writedelay command-line switch

Some "bad" UARTs (for example USB-to-Serial adapters or embedded ARM UARTs) require additional delay after each written serial command/block.

This is a workaround to UARTs poor buffering behaviour; which can not be easily fixed by modifying lpc21isp UART initialization code.

This patch allows using lpc21isp with Prolific USB-to-serial adapters and various embedded ARM linux boards (BeagleBone, BeagleBoard, Raspberry Pi etc.)

With -writedelay parameter the lpc21isp adds 100ms delay after each written serial data block.

(This pull request also includes Makefile changes for OS X compilation support; sorry for that)