add re.nostr for the empty regular expression; add re.allchar for the regular expresssion containing all charactors
a new regular expression engine for solving both positive and negative membership constraints
minor clean-up, bring back derivatives
add re.nostr for the empty regular expression; add re.allchar for the regular expresssion containing all charactors
Merge branch 'master' of github.com:tiliang/CVC4
More useful error message when someone tries mkExpr(VARIABLE).
Suggest command-line options on typos