re_intuit_start(): use the rx_origin var more

re_intuit_start(): use the rx_origin var more

Make the rx_origin variable (introduced in the previous commit, and which
specifies the current minimum legal place the regex could match at) to
also be used at the start and end of the "other" substr match: the origin
is now passed in this var to the other parts of the code that use it,
rather than in the anonymous "t" variable, which is slowly being reduced
in function to a temporary generic char pointer.