fd leak

[jbenet]

We're leaking fds (in linux only i think?). It may be related to our use of reuseport. Though leveldb is a bit suspect too (must make sure we close the queries).

[jbenet]

Related to #690

[whyrusleeping]

This is the biggest issue im running into now. All the machines i have will eventually hit a limit and crash within a day or two. @zignig and @travisperson both have good logs showing massive amounts of open file descriptors. Im going to assign this one to alpha priority.