Simplify OpenSSL checks in crypt.py.

[craigcitro]

Previously, when confirming OpenSSL is installed, we checked that the module
was installed, and verified that crypto.py was contained in the package
directory.

However, this can cause issues in cases of non-standard installs. In addition,
the imp.find_module call already raises an ImportError in the case that
the module is missing, so this second check isn't needed.

Instead, we just drop the explicit check for crypto.py in the OpenSSL
directory.

PTAL @dhermes

[coveralls]

Coverage decreased (-0.03%) to 65.12% when pulling a687e96 on craigcitro:crypto_check into e7340f3 on google:master.

[dhermes]

@craigcitro I looked at #159 and didn't find any discussion, but I'm fairly certain that imp.find_module does not throw an ImportError in all cases, so your proposed fix doesn't work. I'm going to dig around and report back.

[dhermes]

I'm fairly certain I used http://stackoverflow.com/q/14050281/1068170 as my reference and also recall using pkgutil before deciding on imp.

It seems the most reasonable explanation for

if not os.path.isfile(os.path.join(_package_dir, 'crypto.py')):

is to verify that the removed line

from OpenSSL import crypto

still works. Testing out in 0.13 instead of 0.14 it seems that OpenSSL.crypto comes via crypto.so instead of crypto.py:

~/Desktop $ virtualenv venv
~/Desktop $ source venv/bin/activate
(venv) ~/Desktop $ pip install pyOpenSSL==0.13
Collecting pyOpenSSL==0.13
...
(venv) ~/Desktop $ ls -1 venv/local/lib/python2.7/site-packages/OpenSSL/
crypto.so*
__init__.py
__init__.pyc
rand.so*
SSL.so*
test/
tsafe.py
tsafe.pyc
version.py
version.pyc
(venv) ~/Desktop $ cat venv/local/lib/python2.7/site-packages/OpenSSL/version.py
# Copyright (C) AB Strakt
# Copyright (C) Jean-Paul Calderone
# See LICENSE for details.

"""
pyOpenSSL - A simple wrapper around the OpenSSL library
"""

__version__ = '0.13'

[dhermes]

@craigcitro WDYT of all that?

[craigcitro]

@dhermes I guess I'm confused - the python docs explicitly say find_module will throw if the module isn't found, and that SO link only mentions a problem for dotted modules.

where will this fail?

[dhermes]

Yeah you can disregard my first comment. It's safe(ish, mostly) to say that it will throw when it doesn't exist.

More WDYT of the check of OpenSSL.crypto and the original intent of the code.

[craigcitro]

do we think there's a case where someone could have OpenSSL installed by not have an OpenSSL.crypto module?

[dhermes]

No I don't think so. The flipside: we could check for crypto.py OR crypto.so.