R/W is connected to pin5 aka P1.
ok so R/W is hooked up to the PCF8574. Most backpacks are this way.
I have gone ahead and done all the library related things you have listed. As I mentioned, I had replaced my sketch-LiquidCrystal_I2C directory with the contents fm's library. I have now deleted both the sketch and the IDE LiquidCrystal directories and unzipped (the non-MAC) files into an IDE directory called LiquidCrystal. It seems to be working. During detection now, the backlight is on as well as all of the LCD dots. Is it supposed to be like that?
Not sure what you mean by "It seems to be working" or "During detection now, the backlight is on as well as all of the LCD dots".
When the LCD powers up before it is initialized, one row of characters on a 16x2 LCD will be "blocks" with all pixels for each character position turned on. The other row will have its pixels off.
Once the LCD is properly initialized all the pixels will be cleared.
The guesser sketch attempts to initialized the LCD and then print the constructor on the display.
I'm glad the instructions on installing this library are clear as mud. LOL.
Part of the problem is that the Arduino guys change the IDE constantly (way too often in my opinion) so it can be difficult to make one set of instructions that can work for different releases of the IDE.
There are also some things that can make things easier on newer releases that don't work on the older releases.