Auto merge of #3783 - Enet4:patch-1, r=Manishearth
Auto merge of #3783 - Enet4:patch-1, r=Manishearth

Update why transmute_int_to_float is bad

As suggested in #3550, this PR changes the reason why using `transmute` from an integer to a float is not recommended. Effectively, `from_bits` uses `transmute` underneath, but the former is preferred.

aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust