add find_first function (Trac #1738) #2333

Original ticket http://projects.scipy.org/numpy/ticket/1738 on 2011-02-09 by @nbecker, assigned to unknown.

find_first would be a performance enhancement. The current alternative would be something like:

argmax (some boolean function...)

which requires a lot of extra work if all you want is the index of the first occurance.

This is frequently wanted for 1-d arrays, where it's meaning is unambiguous. I think semantics for n-d (n > 1) arrays is up for discussion.