Add in a function to do file length.
Add in a function to do file length.

This makes it a little more generic, since we no longer
depend on fp.fileno().

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@irobot.com>

manuelnaranjo/git-got,jake4679/git-got