fixed cp35135 - re extension flag can contain multiple letters

all processed re extension flags are removed once converted to option

The semantic of the (?iLmsux) options in python apply to entire re. Once set, it can not be changed. https://docs.python.org/2/library/re.html#regular-expression-syntax

In case of c# regex  (?imnsx-imnsx) options can be turned on/off and apply until the end of enclosing group or subexpression only. http://msdn.microsoft.com/en-us/library/x044wc7s%28v=vs.100%29.aspx
Since the options are detected and captured, there is no point of keeping them in expression.