does SPIRONOLACTONE / ALDACTONE contain progestin?

No, spironolactone/Aldactone pills contain only one chemical — spironolactone.

Spironolactone works by inhibiting aldosterone, which is a naturally-occuring steroid-based hormone responsible for water/mineral regulation in the kidneys. This is why the main use of spironoactone is as a diuretic ("water pill"), which makes people pee more.

Unfortunately, our body uses steroid-based hormones for many different bodily functions. And since all these hormones are all based on the steroid molecule (4 rings, 3 of which are 6-sided, and one five-sided), they look very much alike.

Steroid: http://en.wikipedia.org/wiki/Steroid
Aldosterone (hormone in charge of water/mineral regulation): http://en.wikipedia.org/wiki/Image:Aldosterone.svg
Dihydro-testosterone (an androgen, which is a male sex hormone): http://en.wikipedia.org/wiki/Dihydrotestosterone

Because of their structural similarity, spironolactone not only inhibits aldosterone, it also inhibits dihydro-testosterone, a male sex hormone.

As a result, spironolactone causes "feminizing" side effects such as gynecomastia (enlargement of breasts), menstrual irregularities and testicular atrophy. This is probably why some people mistakenly conclude that spironolactone contains female sex hormones (such as progestin), when it absolutely does not.

Hope that helps.

Spironolactone is very simular to progesterone, chemically. There is only a few differences when you look at the molecules. See:
http://www.thebestlinks.com/images/thumb/4/4e/200px-Spironolactone.png
http://userwww.service.emory.edu/~rherman/progesterone.gif
But the hormonal effect are different.
Spironolactone does indeed have progestational (like progesterone) effects but not much. Its main effect is as an Anti-mineralocorticoid (affecting the kidney). It also has Anti-androgenic (blocking androgens) effects. That is why it helps to grow back hair.