RegExp to string, the default regexp.toString() will output a different string in nodejs and iojs/chrome.
reg2str - output all RegExp's string like iojs/chrome in all javascript enviroment.
new RegExp('/').toString() ==> "/\//"
a = '\\' ==> string literal: '\'
a.length ==> 1
new RegExp('/').toString() ==> "///"
a = '\\' ==> string literal: '\\'
a.length ==> 1
reg2str(new RegExp('/')) ==> "/\//"