RAT_LEFTB() Determines if the left mouse button has been
 pressed

 Returns
 <lHasBeenPressed> => left mouse button has been
 pressed

 Syntax
 RAT_LEFTB()

 Description
 This returns .t. if the left button has been pressed
 since last call to this function. Row and column are recorded
 for reference by rat_rowl() and rat_coll().

 Examples
  if rat_leftb()

    ?"While you were out:"

    ?"Left button was depressed at"

    ??rat_rowl(),rat_coll()

  endif

 Notes:
 This is different from RAT_LBHD() in that RAT_LBHD()
 is a 'right now' function - determining if the button IS
 depressed, whereas this function determines if the button HAS
 been depressed.

 Source: S_MOUSE.ASM