fexp is a testing utility, including it in the regular Go build confuses
some automation as it can think it's part of chasquid proper.
All other testing utilities are ignored via the "+build ignore"
annotation for this reason, so this patch adds it to fexp to fix this
issue.
This patch removes the dependency on wget for fetching content over
http, which was used in one of the tests to do some checking on debug
and metric pages, as well as loop detection.
Instead of wget, we now use a small built-in utility called fexp.
