AUTO_ARDUINO_VERSION proposed fix (mk2)

Here's my fix (along with @matthijskooijman) for issue #65

Essentially it adds another sed pass to remove the 1: prefix from Debian version strings (starts with any single number followed by a colon)

It works for me on Debian with 0.10-5 and IDE 1.0.5 e.g. "1:1.0.5+dfsg2-1" becomes "105", it won't break other version detection, e.g. "1.0.1" still becomes "101", "0023" becomes "002"

@matthijskooijman - i managed to clean my repo up, so this replaces [pull #67](https://github.com/sudar/Arduino-Makefile/pull/67)