add filterlim rules for unary minus and inverse

rename filter_lim to filterlim to be consistent with filtermap

add check to Cooper's algorithm that left-hand of dvd is a numeral

merged

robust writing of MaSh state -- better drop learning data than cause other problems in Sledgehammer

avoid odd warnings due to failure of systray icon;

synchronized read access to cache file -- avoid potential conflict with ongoing write (which is non-atomic); clarified signature -- cache init is unsynchronized and hopefully used at most once per file;

tuned;

recovered error to finish proof (e.g. bad obtain export) from 223f18cfbb32; tuned message;

semi-automated Cygwin setup;