BedTool.__len__ leaks file descriptors

[daler]

The following code illustrates the leak:

import pybedtools
fn = pybedtools.example_filename('a.bed')
orig_fds = pybedtools.helpers.n_open_fds()

# no len()
n1 = []
for i in range(100):
    x = pybedtools.BedTool(fn)
    n1.append(pybedtools.helpers.n_open_fds())
print max(n1) - orig_fds
#2

# check len() each time
n2 = []
for i in range(100):
    x = pybedtools.BedTool(fn)
    len(x)
    n2.append(pybedtools.helpers.n_open_fds())
print max(n2) - orig_fds
#100

[daler]

fixed in adc0195