TextMode procedure

  DECLARATION:  TextMode(Mode : Word);

      PURPOSE:  Selects a specific text mode

         UNIT:  CRT

      REMARKS:  When TextMode is called, the following actions occur:

                   - The current window is reset to the entire screen
                   - DirectVideo is set to TRUE
                   - CheckSnow is set to TRUE if a color mode was selected
                   - The current Text Attribute is reset to normal
                     (corresponds to a call to NormVideo)
                   - The current mode is stored in LastMode

                A call to TextMode(LastMode) will cause the last active
                text mode to be re-selected.  The following constants are
                defined in the CRT Unit:

                   Const

                      BW40  = 0;        { 40 X 25 B/W on a color adapter }
                      BW80  = 2;        { 80 X 25 B/W on a color adapter }
                      Mono  = 7;   { 80 X 25 B/W on a Monochrome adapter }
                      CO40  = 1;      { 40 X 25 color on a color adapter }
                      CO80  = 3;      { 80 X 25 color on a color adapter }
                      Font8x8 = 256;            { EGA/VGA 43 and 50 line }
                      C40 = CO40;          { For Turbo 3.x compatibility }
                      C80 = CO80;          { For Turbo 3.x compatibility }