-w flag never actually checked s3 for a file's existence. Always refused to upload.
added non-zero exit statuses for unsuccessful runs

Previously, the program always exited 0 unless it crashed.  This covered many of the failure scenarios like "permission denied" and "The specified bucket does not exist", but didn't cover anything that would provoke usage() to be called ("-h" notwithstanding)

This adds an arbitrarily ascending list of non-zero exit codes to all the cases of "usage" and also the exit() called for unaviliable multi-part upload.  usage() not defaults to exit status 1, since -h has been covered and most other uses of usage() would be for error conditions
New method: modify_network_interface_attribute

Adding the modify_network_interface_attribute method on ec2 connection.
Allows users to modify various attributes of an ENI.

Addresses issue #1426
PEP8 and other style fixes to fit in with existing code.
Add a check to ensure a valid boolean, "true" or "false" are sent for boolean values before doing a call to the server.
Add modify_network_interface_attribute unit tests.
Test PEP8 line length fixes
Update distribution.py

Fix flipped enable/disable pydoc
Merge pull request #1657 from lorrin/develop

Update distribution.py to fix flipped enable/disable pydoc
Merge pull request #1637 from jerm/fix_no_overwrite_and_exit_statuses

Fix bug in -w and added exit statuses for unsuccessful runs
Merge remote-tracking branch 'taylordt/modify-network-interface-attrib' into develop