https://arduino-info.wikispaces.com/LCD-Blue-I2C
to enable a 1602A 16x2 LCD that has an I2C adapter board attached.
Note: you need to use version 1.21, not the later ones.
I just got it running, but I'll post more details as I progress. I'm expecting some of the 0.96" OLED displays this week, so I'd like to make it such that either type of display can be utilized. Since Michael just added OLED support, I figured it was a good time to play with the 1602A unit while I wait.
Update: I duplicated the functionality of oledprint/oledcls/oledsend into new commands lcddprint/lcdcls/lcdsend for the 1602a display. Tomorrow I should have a .96 oled to test with, so as soon as I can test running both displays chained on I2C at the same time, I'll submit a patch. I tossed in a lcd backlight on/off command as well.
For those who may be interested in advance, heres a patch against ver 1.41: