def path_debase(aPath,aBase)
			aBase = append_slash(aBase)
			aPath = remove_slash(aPath) unless aPath=='/'
			aPath[0,aBase.length]==aBase ? aPath[aBase.length,aPath.length-aBase.length] : aPath
		end
def path_debase(aPath,aBase)
			aBase = append_slash(aBase)
			aPath = remove_slash(aPath) unless aPath=='/'
			aPath[0,aBase.length]==aBase ? aPath[aBase.length,aPath.length-aBase.length] : aPath
		end
def ensure_prefix(aString,aPrefix)
	aString.begins_with?(aPrefix) ? aString : aPrefix+aString
end

def ensure_suffix(aString,aSuffix)
	aString.ends_with?(aSuffix) ? aString : aString+aSuffix
end
 Remove base dir from given path. Result will be relative to base dir and not have a leading or trailing slash
'/a/b/c','/a' = 'b/c'
'/a/b/c','/' = 'a/b/c'
'/','/' = ''