Fixed issue in a corner case of set_selinterval, when inserting boundary markers.
Fixed a bug in utl_buffer (oversight after major feature push).
Made set_selinterval support general ranges (including overlapping and reversed).
Implemented set_selepos without pop_select.
Updated various toolbox functions to use the new set_selinterval and set_selepos.
Rewrote flt_selchans without pop_select, replaced instances of pop_select of channels throughout the toolbox.
Implemented flt_window without pop_select (epoch sub-range selection).
Fixed some teething issues in updated set_new and set_selepos.
Tweaked set_insert_markers update.