* l = the lag (positive or negative, if you want to extend bounds in the past)
Output
* bounds_out = the lagged bounds
DESCRIPTION
Cuts the bounds at the start of the period. If the lag is negative, then bounds are extended in the past for a number of peridos equal
to the absolute value of the lag.
EXAMPLE
lagbounds(['1985q2';'1997q4'],3)// Provides the (2x1) vector:// ['1986q1'// '1997q4']grocer_boundsvar=lagbounds(grocer_boundsvarb,-grocer_l-1)// taken from function cadf