Not to be contrary, but there •is• a definition of gruntle that is the very opposite of disgruntle, but the word may have gone out of useage, due to the fact that it usually conjures the noise of pigs snorting:-D
I'd include the url of the website that I'm referring to, but I fear that it wouldn't be appropriate to do here, but trust me that to be gruntled is synonomous with being happy.
gruntle
v : cause to be more favorably inclined; gain the good will of; "She managed to mollify the angry customer" [syn: pacify, lenify, conciliate, assuage, appease, mollify, placate, gentle]
Source: WordNet ® 2.0, © 2003 Princeton University
http://dictionary.reference.com/search?q=gruntle