[imps] content type sniffing - stream length

[Ryan King]

"2.7.4 Content-Type sniffing: unknown type" says:

   2. If pattern length is smaller than stream length then skip this  
row.

..which doesn't seem to make sense, since the streams will likely be  
512 bytes long, and the patterns are a handful of bytes each. I  
suspect that the intent was the opposite:

   2. If stream length is smaller than pattern length then skip this  
row.

-ryan